Deepwater Horizon Disaster

Deepwater Horizon oil spill


Revised 15 October 2010

The Deepwater Horizon oil spill (also known as the Gulf of Mexico Oil Spill or the BP Oil Spill) is the largest marine oil spill in history, and was caused by an explosion on the Deepwater Horizon offshore oil platform about 50 miles southeast of the Mississippi River delta on April 20, 2010 (28.74°N, 88.39°W). Most of the 126 workers on the platform were safely evacuated, and a search and rescue operation began for 11 missing workers. The Deepwater Horizon sank in about 5,000 feet (1,500 m) of water on April 22, 2010. On April 23 the U.S. Coast Guard suspended the search for missing workers who are all presumed dead. After a series of failed efforts to plug the leak, BP said on July 15 that it had capped the well, stopping the flow of oil into the Gulf of Mexico for the first time in 86 days.

BP was principal developer of the Macondo Prospect oil field where the accident occurred. The Deepwater Horizon, owned by Transocean Ltd., was under a contract with BP to drill an exploratory well. BP was the lessee and principal developer of the Macondo Prospect oil field in which the rig was operating. At the time of the explosion, BP and Transocean were in the process of closing the well in anticipation of later production. Halliburton had recently completed cementing of casings in the well. The U.S. Government named BP as the responsible party in the incident and will hold the company accountable for all cleanup costs resulting from the oil spill. BP has accepted responsibility for the oil spill and the cleanup costs.  However, in a report issued on September 18, 2010, BP clearly indicated its view that Transocean and Halliburton deseved considerable blame for the disaster, allegations vehemently denied by those companies

The sinking of the platform caused crude oil to gush out of the riser — the 5,000-foot pipe that connects the well at the ocean floor to the drilling platform on the surface. Attempts to shut down the flow failed when a safety device called a blowout preventer (BOP) could not be activated.

The rate of oil release became a the subject of intense debate. Throughout the first month of the spill, government responders officially adhered to what we now know were low and inaccurate estimates. Non-governmental scientists, on the other hand, used the small amount of publicly available flow data to generate estimates that have proven to be much more accurate. Live video feeds of the leak from the ocean floor fueled the controversy over the magnitude of the leak.

The emerging consensus is that roughly five million barrels of oil were released by the Macondo well, with roughly 4.2 million barrels pouring into the waters of the Gulf of Mexico.

Prior to the Deepwater Horizon, the largest oil spill in U.S. waters was in 1968 when the tanker Mandoil II spilled about 300,000 barrels into the Pacific Ocean off Columbia River near Warrenton, Oregon. The 1989 wreck of the Exxon Valdez released about 261,905 barrels (11 million gallons) of crude oil into Prince Williams Sound in Alaska. In 2005, Hurricane Katrina caused a spill of eight million gallons of crude and refined oil products from many different point sources into the southern corridor of the Mississippi River and the Gulf of Mexico. In 1979-80, the Ixtoc 1 exploratory well operated the PEMEX, the Mexican national oil corporation, experienced a blowout and ultimately released about 3.3 million barrels (140 million gallons) of crude oil into the Bay of Campeche in Mexico.

caption The Deepwater Horizon oil platform ablaze on April 21, 2010. Credit: U.S. Coast Guard.

The oil slick produced by the Deepwater Horizon oil spill covered as much 28,958 square miles (75,000 square kilometers), an area about the size of South Carolina, with the extent and location of the slick changing from day to day depending on weather conditions.  By the first week in June, oil had come ashore in Louisiana, Mississippi, Alabama and Florida, with significant wildlife fatalities in Louisiana. In the weeks following the accident, scientists discovered enormous oil plumes in the deep waters of the Gulf of Mexico, raising concerns about ecological harm far below the surface that would be difficult to assess.

The surface slick threatened the ecosystems and the economy of the entire Gulf Coast region. The U.S. Fish and Wildlife Service reported that up to 32 National Wildlife Refuges were potentially affected by the spill. Concerns were raised about the environmental impacts of chemicals known as dispersants that have been used to dissipate the oil slick.  By June 2, 2010,  the National Oceanic and Atmospheric Administration (NOAA) had banned fishing in about 36% of federal waters, or 86,895 sq mi (229,270 sq km) of the Gulf. 

By June 9, BP stock had lost close to half its value, more than $82 billion, in the seven weeks since the spill started, although the stock rebounded somewhat on the fall of 2010. According to BP, the cost of the response to September 29 amounted to approximately $11.2 billion, including the cost of the spill response, containment, relief well drilling, static kill and cementing, grants to the Gulf states, claims paid and federal costs.

The three month saga of BP's attempts to stem the flow of oil made it clear that the oil industry's impressive ability to extract oil from ever deeper offshore environments had not been accompanied by an equally effective capability to predict and respond to accidents. As drillers pushed the boundaries, regulators didn't always mandate preparation for disaster recovery or perform independent monitoring. Documents and testimony from Congressional hearings revealed a series of potential failures and warning signs at the well site in the hours leading up to the rig explosion, as well as questions that had been raised years earlier about the reliability of deepwater technology and the ability of the industry to deal with "worse-case scenarios" of accidents. The Minerals Management Service, the government agency with lead oversight of offshore oil and gas activity, came under heavy criticism for lax environmental planning and for sacrificing sound stewardship of a public natural resource for the narrow economic gain to private industry.

Deepwater Horizon

caption The Deepwater Horizon before the disaster. Credit: Transocean.

Deepwater Horizon was an ultra-deepwater, dynamically positioned, column-stabilized, semi-submersible mobile offshore drilling unit (MODU).  The rig was 396 feet (121 m) long and 256 feet (78 m) wide and could operate in waters up to 8,000 feet (2,400 m) deep, to a maximum drill depth of 30,000 feet (9,100 m). Built by Hyundai Heavy Industries in South Korea and completed in 2001, the rig was owned by Transocean Ltd. and leased to BP until September 2013.  At the time of the explosion, the rig was on BP's Mississippi Canyon Block 252, referred to as the Macondo Prospect, in the United States sector of the Gulf of Mexico, about 41 miles (66 km) off the Louisiana coast.  The rig commenced drilling in February 2010 at a water depth of approximately 5,000 feet (1,500 m).  The well was planned to be drilled to 18,000 feet (5,500 m), and was to be plugged and abandoned for subsequent completion as a subsea producer.

Explosion and fire

The fire aboard the Deepwater Horizon reportedly started at 9:45 p.m. CST on April 20, 2010. Survivors described the incident as a sudden explosion that gave them less than five minutes to escape as the alarm went off. Video of the fire shows billowing flames, taller than a multistory building.  After burning for more than a day, Deepwater Horizon sank on April 22, 2010.

caption Firefighters combat the fire on the Deepwater Horizon. Credit: U.S. Coast Guard.

The precise cause of the explosion and fire that led to the oil spill are under investigation.  The current hypothesis about the chain of events is as follows. Transocean, Ltd., representatives said workers had been performing their standard routines with "no indication of any problems" just prior to the explosion. At the time of the explosion the rig was drilling but was not in production. Production casing was being run and cemented at the time of the accident. Once the cementing was complete, it was due to be tested for integrity and a cement plug set to temporarily abandon the well for later completion as a subsea producer. Halliburton said that it had finished cementing 20 hours before the fire. Interviews with rig workers suggest that a bubble of methane gas escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before exploding. Transocean chief executive Steven Newman stated: "there was a sudden, catastrophic failure of the cement, the casing or both."

Casualties and rescue efforts

At the time of the explotion there were 126 people on the Deepwater Horizon platform; of these, 115 individuals were evacuated. Most of the workers evacuated the rig and took diesel-powered fiberglass lifeboats to the M/V Damon B Bankston, a workboat that BP had hired to service the rig; some were then evacuated from the workboat by helicopter to regional trauma centers. The United States Coast Guard launched a rescue operation involving two cutters, four helicopters and a rescue plane. After a three-day search covering 5,300 miles, the Coast Guard called off the search for the 11 missing persons, concluding that the "reasonable expectations of survival" had passed. Officials concluded that the missing workers may have been near the blast and not been able to escape the sudden explosion.

Estimating the magnitude of the spill

Main article: Estimating the oil flow rate from the BP Macondo well

The federal government’s and BP’s estimates of the amount of oil flowing into and later remaining in the Gulf of Mexico in the aftermath of the Deepwater Horizon explosion were the source of significant controversy, which undermined public confidence in the federal government’s response to the spill. By initially underestimating the amount of oil flow and then, at the end of the summer, appearing to underestimate the amount of oil remaining in the Gulf, the federal government created the impression that it was either not fully competent to handle the spill or not fully candid with the American people about the scope of the problem.

caption A video of the oil leak taken by a remotely operated underwater vehicle. Credit: PBS.

The First Month

Throughout the first month of the spill, government responders officially adhered to what we now know were low and inaccurate estimates. Non-governmental scientists, on the other hand, used the small amount of publicly available flow data to generate estimates that proved to be much more accurate

The Government’s Estimates

As a first step in determining whether, or how much, oil was flowing from the Macondo well, BP enlisted remotely operated vehicles (ROVs) to investigate the immediate wellhead area. These ROVs did not uncover any leaks. Rear Admiral Mary Landry, the Federal On-Scene Coordinator (and ranking federal official on the spill response team at the time), told CBS News on April 23, 2010, that “at this time there is no crude emanating from that wellhead at the ocean floor . . . . there is not oil emanating from the riser either.”

But at the time of Admiral Landry?s statement, the riser had not yet been inspected. Over the next 24 hours, BP’s ROVs traced the riser from the wellhead to where the Deepwater Horizon rig had come to rest, approximately 1,500 feet from the blowout preventer (BOP). The ROVs discovered two leaks, one from a kink in the riser above the BOP (“kink leak”) and a primary leak from the end of the riser, where it had broken off from the rig.

After the discovery of these leaks on April 24, 2010, Coast Guard and BP officials put out an estimate: Up to 1,000 bbls/day were flowing from the two leaks in the riser. Neither the Coast Guard nor BP divulged the data or methodology behind this estimate. It appears the figure came from BP without supporting documentation.

In the spill’s second week, the official flow-rate estimate increased from 1,000 bbls/day to 5,000 bbls/day as a result of input from the National Oceanic and Atmospheric Administration (NOAA). On April 28, 2010, Admiral Landry stated that “NOAA experts believe the output could be as much as 5,000 barrels.”

Based on the information currently available to Commission staff, the source of the 5,000 bbls/day estimate appears to have been an unsolicited, one-page document emailed to Admiral Landry?s Scientific Support Coordinator on April 26, 2010, by a NOAA scientist. The NOAA scientist?s 5,000 bbls/day estimate did not take into account the kink leak, and his methodology for estimating the velocity of the leaking oil was imprecise.17 Further, there is no indication that the scientist had expertise in estimating deep-sea flow velocity from video data or that he used an established or peer-reviewed methodology when doing so.

Despite the acknowledged inaccuracies of the NOAA scientist?s estimate, and despite the existence of other and potentially better methodologies for visually assessing flow rate (discussed below), 5,000 bbls/day was to remain the government?s official flow-rate estimate for a full month, until May 27, 2010.

Non-governmental Estimates

From the outset, estimates from non-governmental sources were significantly higher than official government estimates. In at least some instances, the cause of the discrepancy appears to be that non-government scientists relied on more refined or better-established methodologies.

caption Oil from the Deepwater Horizon spill pools against the Louisiana coast along Barataria Bay. Credit: Associated Press

Estimates Based on Satellite Imagery

The first independent flow-rate estimate surfaced on April 27, 2010, at the time the official estimate was 1,000 bbls/day. Using publicly available satellite images, John Amos, the founder of, estimated the leak size to be at least five times the government estimate—5,000 to 20,000 bbls/day.  Amos generated the low number in his range by multiplying the surface area of the spill by what he considered the minimum thickness for oil to be visible on the Gulf?s surface (1 micron). He then generated the high number by relying on a BP statement that 3% of the slick was significantly thicker (100 microns).

On May 1, 2010, Dr. Ian MacDonald (a Florida State University oceanographer) published a new estimate on Based on a Coast Guard map that tracked the spill?s surface size and classified the color of the surface oil throughout, Dr. MacDonald generated a flow estimate of 26,500 bbls/day using the Bonn Convention. Like Amos, he assumed that none of the oil had burned, evaporated, dispersed, been skimmed, or was then below the surface.

Estimates Based on Video of the Flow

On May 12, 2010, BP released a thirty-second video of oil coming out of the end of the broken riser—a crucial piece of data. As discussed above, the government?s estimate of 5,000 bbls/day appears to have been based on visual observation of flow from the riser. Within 24 hours, at least three scientists had used various methodologies to derive estimates of the flow rate substantially greater than the government?s then-current estimate.  Dr. Timothy Crone, a marine geophysicist at Columbia University?s Lamont-Doherty Earth Observatory, estimated that 50,000 to 100,000 bbls/day of total flux were flowing out of the end of the riser.  Dr. Eugene Chiang, an astrophysicist at the University of California at Berkeley, estimated the total flux from the end of the riser to be between 20,000 and 100,000 bbls/day. Dr. Steven Wereley, a mechanical engineer at Purdue University and expert in fluid mechanics, estimated that the total flux from the end of the riser was 72,179 bbls/day (±20%).

All of these non-government figures estimated the total flux being released from the end of the riser, which includes both oil and natural gas.  If we were to assume the then-current understanding that the flux was 50% oil, the Crone, Chiang, and Wereley estimates would be, respectively: 25,000-50,000 bbls/day; 10,000-50,000 bbls/day; and 36,090 bbls/day. The Crone, Chiang, and Wereley estimates did not include flow from the kink leak, for which there was then no public data.

BP attempted to dismiss the Crone, Chiang, and Wereley estimates. It told National Public Radio on May 13, 2010, that “there?s no way to estimate the flow coming out of the pipe accurately.”

The Crone, Chiang, and Wereley estimates proved to be significantly more accurate than the official estimates. The government?s 5,000 bbls/day figure, derived from the same type of visual observation as the Crone, Chiang, and Wereley estimates, appears to have been based on a cruder methodology than at least Crone?s and Wereley?s.  The government appears to have taken an overly casual approach to the calculation and release of the 5,000 bbls/day estimate—which, as the only official estimate for most of May, took on great importance.

BP was subject to intense pressure and criticism that it was impeding independent scientific inquiry into the leak. Rep. Edward J. Markey (Massachusetts) sent a direct request to BP America’s CEO Lamar McKay to release more video footage. Bowing to this pressure, BP announced on May 19, 2010 that there will be a live feed of the oil spill made publicly available on the web--an oil gusher webcam. BP said they would release the feed, which went live on May 20, 2010 at the web site of the U.S. House of Representatives' Select Committee for Energy Independence and Global Warming. Heavy traffic caused the web site to crash.

The Flow Rate Technical Group

On May 19, 2010, the National Incident Command spearheaded the creation of an inter-agency Flow Rate Technical Group (Flow Rate Group) and charged it with generating (1) a preliminary flow rate as soon as possible and (2) a final flow-rate estimate based on peer reviewed methodologies within two months. On May 23, 2010, Dr. Marcia McNutt, Director of the U.S. Geological Survey and Science Advisor to the Secretary of the Interior, was appointed the Group?s leader. The Flow Rate Group enlisted non-governmental scientists with applicable expertise and experience, including Dr. Wereley, a critic of the low early estimates. The Group?s initial estimates, however, proved chronically low, too. Moreover, the Group?s later, more accurate estimates relied primarily upon data collected by a team led by Secretary of Energy Dr. Steven Chu and a team from the Woods Hole Oceanographic Institution, though the Group did play a significant role in analyzing and interpreting this data.

May 27, 2010 Estimate (12,000-25,000 bbls/day)

The Flow Rate Group published its first estimate on May 27, 2010, noting that “[t]he only range of flow rates that is consistent with all 3 of the methods considered by the [the Group] is 12,000 to 19,000 barrels per day. Higher flow rates [of up to 25,000 bbls/day] are consistent with the data considered by [the Plume Team].” A few members had also produced maximum estimates, several of which were in excess of 50,000 bbls/day, but this upper bound was not released. The Plume Team?s report originally contained appendices that revealed some divergence of opinion within the Team. The appendices were not publicly released.

June 10, 2010 Estimate (20,000-40,000 bbls/day)

On June 10, 2010, the Flow Rate Group announced a revised flow-rate estimate of 25,000 to 30,000 bbls/day with a lower bound of 20,000 and a higher bound of 40,000 bbls/day.The Group produced a three page document called Pooling Expert Assessments to accompany those estimates. That document provided intervals with high and low numbers from each of six members of the Plume Team, but only after a “statistical procedure” was applied to “reconcile” the different members? full ranges.

The June 10, 2010 press release announced that two new teams had been added to the Flow Rate Group: the Reservoir Modeling Team, which would help determine the rate at which oil flowed from the reservoir into the well, and the Nodal Analysis Team, which would use that information to determine the rate at which the oil traveled through the well and into the Gulf.  These two teams did not contribute to the June 10 or June 15 estimates. Their purpose was to arrive at a peer-reviewed, final estimate, while the Plume and Mass Balance Teams focused on generating preliminary estimates for public release and for use during the spill.

June 15, 2010 Estimate (35,000-60,000 bbls/day)

On June 15, 2010, the Flow Rate Group announced that it had generated a new official flow estimate of 35,000 to 60,000 bbls/day in conjunction with Secretary Chu and Secretary of the Interior Ken Salazar. According to the accompanying press release, the new estimate was “based on a combination of analyses of high resolution videos taken by ROVs, acoustic technologies, and measurements of oil collected by the oil production ship together with pressure measurements inside the top hat.”69 No additional information on methodology was provided.  We now know that the high end of this estimate was accurate because of pressure readings from a sensor that Secretary Chu?s team had BP place in the Top Hat above the blowout preventer on June 13, 2010.

The Current Estimate (52,700-62,200 bbls/day)

The June 15, 2010 estimate was finally updated on August 2, 2010. A press release announced that, at the outset of the spill, the flow rate was 62,000 bbls/day (±10%), but that it had declined to 53,000 bbls/day (±10%) by the time the well had been capped on July 14, 2010. We now understand that Secretary Chu?s team calculated the 52,700 bbls/day figure by taking pressure readings on July 14, 2010, using a sensor inside the capping stack that eventually stopped the flow of oil entirely. Using this information, and modeling backwards, Secretary Chu?s team and the Flow Rate Group together arrived at an estimate of 62,200 bbls/day for the first day of the spill, based on the Woods Hole finding that 43.7% of the total flux was oil.

Given the new figures, the Deepwater Horizon MC252 Gulf Incident Oil Budget concluded that the total amount of oil discharged during the spill was 4,928,100 barrels (± 10%, which gives a range of 4,435,290 to 5,420,910 total barrels), a number not reduced by the amount of oil captured at the wellhead.

Final Government Estimate Versus Estimates of Independent Scientists

The flow-rate estimates of non-governmental scientists, generated since the well was capped, are useful in assessing the accuracy and durability of the government?s current figures.

caption Estimated flow rate from the Maconda well site. The darker portion of each bar represents the lower bound of a given estimate, while the lighter portion represetns the upper bound. Source: National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling Dr. Timothy Crone and Dr. Maya Tolstoy of Columbia University?s Lamont-Doherty Earth Observatory estimate the total release to be 5,174,887 barrels (± 20%).Their calculations assume that oil represents 40% of the total flux from the well and do not include oil that was released from the kink leak prior to the riser cut on June 3, 2010.81 If the kink leak were taken into account, and the oil ratio was increased to the 43.7% figure generated by the Woods Hole team, this estimate would be on the high end of the government?s current estimate for the total release.

The Woods Hole team also generated an estimate for the total flow from the well with readings from the end of the broken riser and kink leak that were taken using an ROV-mounted acoustic Doppler current profiler to determine velocity, and imaging multi-beam sonar to determine flow volume. The team estimated a total release of approximately five million barrels during the course of the spill.

The emerging consensus is that roughly five million barrels of oil were released by the Macondo well, with roughly 4.2 million barrels pouring into the waters of the Gulf of Mexico. Using different methods, the government teams and independent scientists arrived at the same approximate figure.

Fate of the oil

Geographic extent of the surface oil

caption Cumulative BP / Deepwater Horizon oil slick footprint (red). Analysis by SkyTruth.

Estimates of the extent of the surface oil slick were derived from data on wind and ocean current forecasts, as well as analysis of aerial photography and satellite imagery from a variety of sources. The extents may vary widely from day to day because of changes in wind patterns and ocean currents.  Satellite images analyzed by SkyTruth indicated that the surface slick reached a maximum of 29,000 square miles (75,000 squre kilometers) on May 24. Skytruth estimated the total oil-slick footprint (the area covered at some point in time) at 68,000 square miles (176,119 square kilometers).

The arrival of the oil onshore was different than the iconic images from the Exxon Valdez spill where crude oil from a tanker spilled onto the surface of an enclosed body of water close to a rocky, static shoreline. Instead, the BP spill is pouring millions of gallons from the floor of the Gulf 5,000 feet below in an open sea, and 50 miles from the nearest land, which is composed of broken marshes, river deltas, open bays and barrier islands. The oil arrived in thin lines on the Louisiana coasts, and some scientists predicted a series of "rolling skirmishes" that will last for months, if not years, even after the well is finally capped.

On June 1, 2010, red-brown oil is first appeared on Dauphin Island off the coast of Alabama near the mouth of Mobile Bay, and Mississippi Gov. Haley Barbour said a strand of oil about a meter wide and two miles long has been found on Petit Bois Island near the Mississippi-Alabama border.
caption This map shows the amount of oil on the coastline as reported on July 31 by the federal government based on information from air and ground surveys. For the first month of the spill, the oil stayed mostly in the gulf. But in the last week of May, waves of oil began washing into Louisiana’s fragile wetlands and beaches. In June, oil landings began to be reported more frequently in the states to the east. Survey areas for Louisiana were first released on May 24 and for Mississippi, Alabama and Florida beginning on June 12. Credit: New York Times

On May 19, NOAA concluded that some portion of the oil had reached the Loop Current in the form of "light to very light sheens". The Loop Current is a warm ocean current in the Gulf of Mexico that flows northward between Cuba and the Yucatán peninsula, moves north into the Gulf of Mexico, loops west and south before exiting to the east through the Florida Straits. Once in the Loop Current, oil could be carried into the Florida Keys and the Atlantic Ocean. By May 27, 2010, a change in the current had trapped a slick of oil in a huge circular eddy that scientists said appears likely to push slowly west instead of pumping the oil south into the Florida Keys.

On June 3, scientists at National Center for Atmospheric Research released the results of a computer modeling study that indicates that oil from the spill in the Gulf of Mexico might soon extend along thousands of miles of the Atlantic coast and open ocean as early as the summer of 2010. The computer simulations indicate that, once the oil in the uppermost ocean has become entrained in the Gulf of Mexico’s fast-moving Loop Current, it is likely to reach Florida's Atlantic coast within weeks. It can then move north as far as about Cape Hatteras, North Carolina, with the Gulf Stream, before turning east. Whether the oil will be a thin film on the surface or mostly subsurface due to mixing in the uppermost region of the ocean is not known.

On June 4, 2010, the first significant amount of oil arrived on the Florida coast. State and local officials reported that gooey blobs of oil tar were washing ashore in growing numbers on the white-sand beaches of the Florida Panhandle. 

Underwater plume of oil

On May 12, scientists at the National Institute for Undersea Science and Technology (NIUST) discovered why they described as large oil plumes in the deep waters of the Gulf of Mexico, including one as large as 10 miles long, three miles wide and 300 feet thick in spots. The plumes were recorded at depths of 1,000–1,400 meters. Initial reports suggested that the plumes are depleting the oxygen dissolved in the water column, which could pose a threat to marine life forms at varying trophic levels.

On May 27 2010, scientists from the University of South Florida and the Florida Fish and Wildlife Research Institute reported a new, wide area of “dissolved hydrocarbons” that is about six miles wide, and extends from the surface down to a depth of about 3,200 feet. The plume stretches 22 miles northeast of the blown wellhead toward Mobile Bay, Alabama. Yhey discovered the plume while they were taking water samples in the DeSoto Canyon off the Florida Panhandle. The plume is clear, with the oil entirely dissolved. Scientists need to do more tests to determine whether those hydrocarbons are from the chemical dispersants used to break up the oil, or the emulsification of oil as it flowed away from the well.

A month after the accident, some scientists criticized the government of failing to conduct an adequate scientific analysis of the damage and of allowing BP to obscure the spill’s true scope. They point to a 2003 study by the National Academy of Sciences, which suggested that the oil in a deepwater blowout could break into fine droplets, forming plumes of oil mixed with water that would not quickly rise to the surface. Critics charge that NOAA should have been better prepared to assess the fate and transport of oil below the surface.

On May 30, 2010, scientists from the University of Georgia reported the existence of the underwter plume based on two pieces of evidence. First, data from their Conductivity, Temperature, Depth (CTD) Sensor  indicate a plume that extends from about 1100m to 1300m in the water column. Second, oil was clearly visible in water samples taken within the plume, but absent from samples taken above and below the plume.

On June 8, 2010, NOAA Administrator Jane Lubchenco announced that tests on the samples taken by the University of South Florida research team confirmed "very low" concentrations of subsurface oil at sampling depths ranging from the surface to 3,300 feet at locations 40 and 42 nautical miles northeast of the well sites, and another sampling station at 142 nautical miles southeast of the wellhead. Chemical "fingerprinting" confirmed that the oil 42 nautical miles from the well site was from the BP oil spill source.

On July 24, the  University of South Florida team announced what they claimed was the first conclusive evidence that linked the plumes of microscopic oil droplets drifting in the Gulf o the Deepwater Horizon disaster.  The scientists matched samples taken from the plumes with oil from the leaking well provided by BP.

At the same time, a multiagency report from the federal government described the presence of large plumes of microscopic oil droplets within several miles of the wellhead at a depth of 3,280 to 4,265 feet. Oil concentrations there are as high as 10 parts per million, or the equivalent of one tablespoon of oil in 130 gallons of water. Scientists from NOAA observed that the plumes closest to the well may be concentrated enough to pose a threat to nearby deepwater coral reefs.

While conducting research in the Gulf of Mexico between June 19 and 28, 2010, a research team from the Woods Hole Oceanographic Institution found a continuous plume of highly diffuse hydrocarbons 35 kilometers long, 200 meters high, and 2 kilometers wide, at a depth of approximately 1,100 meters. After determining that the Macondo spill was the source of the plume, the group estimated that the plume likely extended beyond the 35-kilometer boundary of the study. The Woods Hole researchers also examined the biodegradation rate by analyzing oxygen drawdown within the plume. The team was unable to find evidence of “systematic oxygen drawdown,” which suggested that rapid biodegradation might not be occurring.

Oil on the ocean floor

caption A ghost crab eats oil from the Gulf of Mexico spill, shown glowing yellow-orange under ultraviolet light, at Gulf Islands National Seashore near Pensacola, FL. Credit: National Geographic

On August 17, scientists from the University of South Florida reported finding oil in the sediments of the DeSoto Canyon, a fissure that leads from the Deepwater Horizon site to just 40 miles from Panama City Beach. To date that was the the eastern-most location for the occurrence of sub-surface oils. The canyon is an import area that provides nutrient-rich waters that support the spawning grounds of commercially important fish species on the West Florida Shelf. The scientists shined ultraviolet light on the samples, and indirectly detected hydrocarbons in the sample that seem to have the same fluorescent fingerprints as oil from the BP well.  Further tests are needed to confirm this findiing

The Government's oil budget

Main article: BP Deepwater Horizon oil budget

On August 4, 2010, the Obama administration released a report that described the fate of the estimated 4.9 million barrels of oil relased by theDeepwater Horizon disaster.  An interagency team, led by the Department of the Interior (DOI) and the National Oceanic and Atmospheric Administration (NOAA) developed a tool called the Oil Budget Calculator to determine what happened to the oil. The calculator uses the 4.9 million barrel estimate as its input and uses both direct measurements and the best scientific estimates available to date, to determine what has happened to the oil.

The report estimated that burning, skimming and direct recovery from the wellhead removed one quarter (25%) of the oil released from the wellhead. One quarter (25%) of the total oil naturally evaporated or dissolved, and just less than one quarter (24%) was dispersed (either naturally or as a result of operations) as microscopic droplets into Gulf waters. The residual amount — just over one quarter (26%) — is either on or just below the surface as light sheen and weathered tar balls, has washed ashore or been collected from the shore, or is buried in sand and sediments. Oil in the residual and dispersed categories is in the process of being degraded.

The government report was criticized by some scientists and Gulf residents. Residents of Louisiana were skeptical because of the false assurances following Hurricane Katrina, and because the early flow rate estimates from BP and federal agencies turned out to be grossly in error. Some scientists though that the governemt report was premature and used faulty methods. One general point of agreement is that the long-term effects of the spill are unknown, and that it is too early to make any conclusions about the true scale of the damage.Thus, the government report concluded that much of the oil was effectively gone already, and that most of the remaining oil was in a highly diluted form. Many interpreted the report to imply that that future damage from the oil might be less than had been feared.

The "spillcam" phenomenon

One of the most important forces driving the response to the Deepwater Horizon disaster was the "spillcam"--live video footage of the leak and recovery operations that was taken by cameras mounted on the ROVs and streamed live on the Web. Video from the spillcam shaped scientific debate about the extent of the oil release, fueled public outrage towards BP, and emboldened politicians to pressure BP for more data and a faster response.

caption A frame from the high resolution video of oil and gas being released from the severed riser pipe on June 3, 2010. Credit: BP

On May 12, 2010, BP released a 30 second video clip of the leak that was taken by a camera mounted to an ROV, which ignited a debate over the magnitude of the leak. At the request of Senator Bill Nelson (Florida) and Barbara Boxer (California), BP released four videos of the leaks. Rep. Edward J. Markey (Massachusetts) sent a direct request to BP America’s CEO Lamar McKay to release more video footage.  Bowing to this pressure, BP announced on May 19, 2010 that there will be a live feed of the oil spill made publicly available on the web--an oil gusher webcam. BP said they would release the feed, which went live on May 20, 2010 at the web site of the U.S. House of Representatives' Select Committee for Energy Independence and Global Warming. Heavy traffic caused the web site to crash.

On May 21, 2010. PBS’ “Newshour” was among the first to convert the video feed to make it work on most Web browsers; subscribers to the “Newshour” channel on YouTube doubled in 24 hours. Since then thousands of web sites have linked to the video supplied by BP. Within a few days, “BP oil spill live feed” was close to the top of a list of searches on Google.

On June 8, 2010, BP released the first high-quality video if the leak after Sens. Barbara Boxer and Bill Nelson requested "full access to all video" to help independent experts determine the exact rate of oil flowing from the well. The high-resolution video shows the ruptured well two days after robots cut the well's riser pipe in preparation for the containment cap. Some scientists and politicians criticized BP for withholding all the high quality video that would increase understanding of the extent of the leak.

The Spill in Context

Oil enters the marine environment from a variety of natural and human sources. The largest sources from human activity originate in the exploration, production and transportation stages of the oil and gas industry. These include offshore oil platforms, tankers, pipelines, barges, railroads,  trucks and various oil storage facilties. The ten largest individual releases of oil from accidents in the U.S. are:

Rank Date Name Location Size
1 April 22, 2010 Deepwater Horizon Gulf of Mexico, off Louisiana 4,900,000
2 February 29, 1968 Mandoil II Pacific Ocean, off Columbia River, Warrenton, OR 300,000
3 March 24,1989 Exxon Valdez Prince William Sound, Valdez, AK 261,905
4 November 1, 1979 Burmah Agate Gulf of Mexico, off Galveston Bay, TX 254,762
5 February 8, 1968 Pegasus (Pegasos) Northwest Atlantic Ocean, off U.S. east coast 228,500
6 March 26, 1971 Texaco Oklahoma Northwest Atlantic Ocean, off U.S. east coast 225,000
7 November 5, 1969 Keo Northwest Atlantic Ocean, SE of Nantucket Island, MA 209,524
8 December 12, 1976 Argo Merchant Nantucket Shoals, off Nantucket Island, MA 183,333
9 April 4, 1975 Spartan Lady Northwest Atlantic Ocean, off U.S. east coast 142,857
10. October 24, 1966 Gulfstag Gulf of Mexico 133,000


In 2005, Hurricane Katrina caused a spill of about 190,000 barrels (8 million gallons) of crude and refined oil products from many different point sources into the southern corridor of the Mississippi River and the Gulf of Mexico.

Except for theDeepwater Horizon, all of the accdients in the list involve oil tankers. Prior to the Deepwater Horizon, the largest release of oil from a platform accident was the Alpha Well 21 Platform A disaster in 1969--also known as the Santa Barbara oil spill--which released about 100,000 barrels of oil. The Deepwater Horizon passed that mark in the first five days.

Natural seeps

Natural seeps can be thought of as natural springs from which liquid and gaseous hydrocarbons (hydrogen-carbon compounds) leak out of the ground. Oil seeps are fed by natural underground accumulations of oil and natural gas. Satellite images have identified hundreds of areas in the where oil is likley to seep from the Earth's crust into the waters of the Gulf of Mexico. These seeps occur over a wide range of the 615,000 mi² (1.6 million km²) Gulf. A 2003 study by the National Academy of Sciences and a 2009 report by oil spill expert Dagmar Schmidt Etkin indicate that between 560,000 and 1,400,000 barrels per year (1,534 to 3,835 barrels per day) seep into the Gulf of Mexico from natural sources, and presumably have been doing so for millennia.  Dozens of natural seeps have been identified off the coasts of Louisiana and Texas, some in the region of the Deepwater Horizon site.

These natural seeps are quasi-continuous or chronic inputs that represent a "background" rate of oil input that have been in existence for hundreds or thousands of years. As the term "seep" implies, the rate of release from these sources of oil is much smaller than human spills that often release large, concentrated pulses of oil. One of the largest and most intensively studied seepage areas lies off Coal Oil Point, in Santa Barbara County, California. Individual seeps in this area release an estimated 80 to 100 barrels (3,360 to 4,200 gallons) of oil per day; Deepwater Horizon is releasing 35,000 to 60,000 barrels per day. Thus the Deepwater Horizon site releases 9 to 39 times the oil per day compared to that released by natural seeps across the entire Gulf of Mexico.

Natural seeps are not constantly active; the volume of oil released can vary considerably throughout the day and from day to day. As a result, only a small area around the source is actually exposed to "fresh" non-degraded oil, which is its most toxic state.

Marine and coastal organisms and ecosystems presumably have adapted to the natural rate of oil input.  Researchers at Woods Hole Oceanographic Institute and the University of California/Santa Barbara studied natural seeps off the coast of California. They found that as the oil moved upwards in the water column, a wide range of microbes consume the oil and produce intermediate products, and that those intermediate products are then converted by another group of microbes to natural gas and other compounds. Their research suggests that the most volatile components of oil from natural seeps normally stay in the water for between ten hours to five days.

Oil that does make it to the surface from natural seeps can spread out very widely. One gallon of oil can spread out to cover more than a full square mile, forming an extremely thin film on the surface, about one-hundredth of a millimeter thick. Under these conditions, the oil is not hazardous. Some of the oil in that thin sheen evaporates within seconds or minutes after it reaches the surface.

A sudden, concentrated and massive pulse of oil from an event such as the Deepwater Horizon disaster presents a fundamentally more acute stress to marine and coastal systems. The amount, rate and spatial concentration of crude oil released from such an event overwhelm the natural mechanisms of oil dispersal and breakdown, producing the significant ecological effects that we observe.

Attempts to stop the leak

BP's long run plan is to complete so-called relief wells that will intercept the existing wellbore at approximately 12,800 feet below the sea floor. Once that is accomplished, heavy fluids and cement can be pumped down hole to kill the well. BP estimated this process will take at least 90 days. On May 2, 2010, BP began drilling the first deep-water intercept relief well, which is located one-half mile from the Macondo well, in a water depth of roughly 4,990 feet. A second relief well was begun on May 16.

caption A blowout preventer. Credit: Cameron-Nautronix.

BP's engineers sought to cut off the leak by using ROVs to activate the blowout preventer (BOP),  a massive five story, 450 ton stack of shut-off valves, rams, housings, tanks and hydraulic tubing that sits on top of the well. The BOP is designed to quickly shut off the flow of oil or natural gas by squeezing, crushing or shearing pipe if there is a sudden, unexpected spike in pressure. This procedure failed. Early speculation suggested that gas hydrates formed in the BOP, causing it to malfunction.  A gas hydrate is a crystalline solid consisting of gas molecules, usually methane, each surrounded by a cage of water molecules.  It is similar to ice, except that the crystalline structure is stabilized by the guest gas molecule within the cage of water molecules.  Gas hydrates are common when gas and water mix, and are found on the ocean floor where there are low temperatures and high pressure.

On May 7, 2010, BP maneuvered a 98-ton steel containment dome over the worst of the leaks, and planned to funnel the oil through a pipe to the surface, where it would be collected by a drill ship. This procedure failed when the dome’s opening was clogged with gas hydrates. The dome was moved off to the side of the wellhead and is resting on the sea floor.

On May 12, 2010, BP abandoned plans for a second, smaller containment dome or “top hat" cofferdam, a 5-foot-tall, 4-foot-diameter structure that weighs less than 2 tons and would be injected with alcohol to act as an antifreeze to keep its outlet clear of gas hydrates.

The first significant success at reducing the release of oil came on May 17, 2010 when robots inserted a four-inch diameter Riser Insertion Tube Tool (RITT) into the Horizon’s riser (21-inch diameter pipe) between the well and the broken end of the riser on the seafloor in 5,000 feet of water. The RITT was expected to work like a straw, sucking the leaking oil into a tanker waiting on the surface where the oil would be separated and then shipped ashore. BP initially stated that the RITT was recovering 5,000 barrels per day, but on May 21, 2010, BP reduced that estimate, stating that the device was recovering an average of about 2,200 barrels of oil a day. Additional oil continued to flow from the leaks.  BP subsequently reported that from the period from May 17th to May 23rd, the daily oil rate collected by the RITT had ranged from 1,360 barrels of oil per day (b/d) to 3,000 b/d, and the daily gas rate has ranged from 4 million cubic feet per day (MMCFD) to 17 MMCFD. The oil is being stored and gas is being flared on the drillship Discoverer Enterprise, on the surface 5,000 feet above.  The RITT was disabled on the evening of May 25, 2010 in preparation for the "top kill" procedure initiated the following day.

On May 26, 2010, the U.S. government gave BP the approval to proceed with a "top kill" operation today to stop the flow of oil from the damaged well. The procedure is intended to stem the flow of oil and gas and ultimately kill the well by injecting heavy drilling fluids through the blowout preventer on the seabed, down into the well.On May 29, 2010, BP engineers said that the “top kill” technique had failed. Despite successfully pumping of over 30,000 barrels of heavy mud, in three attempts at rates of up to 80 barrels a minute, and deploying a wide range of different bridging materials, the operation did not overcome the flow from the well.

caption The Q4000 drilling rig at the Deepwter Horizon site in the Gulf of Mexico. Credit: Dave Martin/The Associated Press

Simultaneously with the top kill, BP attempted what is known as a “junk shot.” This method involves debris such as shredded tires, golf balls and similar objects being shot under extremely high pressure into the blowout preventer in an attempt to clog it and stop the leak. The process was carried out "a number of times" with the U.S. Coast Guard before BP concluded that it had failed.

After consultation with government officials, BP then decided to move on to another option. The company said its next attempt will be a custom-built cap known as the Lower Marine Riser Package (LMRP) Cap Containment System. This first involves cutting and then removing the damaged riser from the top of the failed Blow-Out Preventer (BOP) to leave a cleanly-cut pipe at the top of the BOP’s LMRP. The cap is designed to be connected to a riser from the Discoverer Enterprise drillship and placed over the LMRP with the intention of capturing most of the oil and gas flowing from the well.

In the wake of BP's unsuccessful attempts, on June 1, 2010, Coast Guard Adm. Thad Allen said that efforts to plug the well were over for the timebeing, and that effort will focus on containing and directing most of the oil to tankers on the surface. Allen acknowledged that this will may not capture all the oil, but the hope is it will capture most of the spill until relief wells cap it permanently.

The next move was a "cut-and-cap" approach. On June 3, 2010, a cap was succesfully placed on top of the BOP after a 20 foot pair of shears had severed the riser from the BOP. About 6,000 barrels were recovered on June 4 and pumped to a recovery ship on the surface. According to BP, by June 8 rate of recovery had risen to about 15,000 barrels per day.

On June 8, the Coast Guard directed BP to develop contingency plans for the collection of oil  brought to the surface in the event of an operational failure or severe weather.

On June 16, 2010, BP began collecting crude oil from a second containment system that is attached directly with pipes and other equipment to the failed blowout preventer. That equipment had already been installed for the failed “top kill” effort weeks ago. The oil is transferred to a ship, the Q4000, which will then clean and burn the oil and gas mixture in a processing device called an EverGreen burner. According to Schlumberger, the device's manufacturer, the EverGreen burner is a single-head, 12-nozzle, well test oil burner for onshore and offshore exploration and development well testing and cleanup that "provides an efficient and cost-effective alternative to oil storage."  The EverGreen burner performs a "fallout-free and smokeless combustion of liquid hydrocarbons."

BP announced that oil stopped flowing at 2:25 p.m. on July 15 after the last of several valves was closed on the cap at the top of the well, marking the first time in 86 days that oil was not flowing into the Gulf.

On August 3, 2010, BP launched a "static kill" attempt.  The method is similar to the top kill that failed in early June and would used existing equipment and plumbing. In the static kill, driiling mud is pumped slower and at lower pressure compared to the top kill because the new cap atop the well had stemmed the flow of oil. After the static kill, BP planned to proceed with killing the well from the bottom with the relief well.

Relief wells

BP's solution to the permanent sealing of the well was to drill a relief well: a well drilled to intersect an oil or gas well that has undergone a blowout. The first relief well began drilling on May 2, and the second began on May 16. On September 15, the first relief well successfully intersected with the blown-out Macondo well at 17,977 feet. The next day, BP began pumping cement into the stricken well to permanently seal it. On September 19 BP declared that the well had been successfully sealed. BP then announced that it would proceed to complete the abandonment of the MC252 well, which includes removing portions of the casing and setting cement plugs. A similar plugging and abandonment of both relief wells will occur as well.

The cleanup

BP assumed responsibility for the initial clean up and mitigation efforts. According to BP Chief Executive, Tony Hayward, "we are taking full responsibility for the spill and we will clean it up and where people can present legitimate claims for damages we will honor them." On April 28, the U.S. military announced it was joining the cleanup operation.

The U.S. government established a "unified command" structure to coordinate the response to the spill. The stated purpose of the unified command is to link the organizations responding to the incident and to provide a forum for those organizations to make "consensus decisions." The Deepwater Horizon Unified Command include BP, Transocean, and the following federal agencies: Minerals Management Service, NOAA, the Environmental Protection Agency (EPA), Homeland Security, the Coast Guard, the Department of the Interior, the Department of State,  the Department of Defense, the Fish and Wildlife Service, the National Park Service, the U.S. Geological Survey (USGS), the Centers for Disease Control (CDC) and the Occupational Safety and Health Administration (OSHA).

As of June 22, the Unifed Command identified these resources employed to respond to the spill:

  • Total response vessels: 6,300
  • Total boom deployed: more than 6.7 million feet (regular plus sorbent boom)
  • Oily water recovered to date: more than 25 million gallons
  • Dispersant used to date: more than 1.345 million gallons
  • Oil reccovered to date: 13.5 million gallons
  • Overall personnel responding: more than 37,000
  • 17 staging areas are in place and ready to protect sensitive shorelines, including: Dauphin Island, Ala., Orange Beach, Ala., Theodore, Ala., Panama City, Fla., Pensacola, Fla., Port St. Joe, Fla., St. Marks, Fla., Amelia, La., Cocodrie, La., Grand Isle, La., Shell Beach, La., Slidell, La., St. Mary, La.; Venice, La., Biloxi, Miss., Pascagoula, Miss., and Pass Christian, Miss.

Controlled burns

caption A controlled burn of surface oil from the Deepwater Horizon oil platform. Credit: U.S. Coast Guard.

On April 28, BP performed the first controlled burn of surface oil, also known as an in situ burn.  Fire booms, U-shaped devices that are towed behind two boats and used to pull oil away from the main spill for safe burning, can be used when seas are below 3 feet and when sufficient amounts of oil can be "corralled." Controlled burns continued to be used at the Deepwater Horizon spill site through mid-May, 2010 when conditions were right. This represents the first on-water in-situ burning at a spill since the 1989 test burn during the Exxon Valdez oil spill, which was the first time a fire-resistant boom was used at a spill.  By June 22, more than 225 controlled burns have been conducted that removed more than 9.3 million gallons of oil from the open water.

Chemical dispersants

The EPA and Coast Guard approved the use of dispersants, a group of chemicals designed to be sprayed onto oil slicks to accelerate the process of natural dispersion. The dispersants used in the Deepwater Horizon clean-up are Corexit 9500 and Corexit EC9527A, also known as deodorized kerosene. The EPA has pre-approved both for emergencies that are three nautical miles (roughly five kilometers ) off the shoreline and in water depths greater than 30 feet (10 meters).  In the weeks following the spill, surface dispersants were applied by aerial means by BP and various federal agencies. By June 16, 2010, 1.3 million gallons of dispersant have been deployed—902,000 on the surface and 423,000 subsea—by far the largest ever use of dispersant in a U.S. oil spill.

Corexit 9500 is known in prior scientific studies to pose a high level of toxicity to primary producer biota in the water column; in addition, it has been shown to accelerate the uptake of certain likely carcinogenic minority components present in petroleum such as napthalene. The dispersants used are approximately 10,000 times more lethal to biota than crude oil itself. Corexit 9500 and Corexit EC9527A, manufactured by an Illinois company, both contain 2-butoxyethanol, a chemical known to cause respiratory and skin irritation effects in humans. These dispersants have been banned for use by the United Kingdom, due to known biological effects on people and natural systems.

Oil spill dispersants do not actually reduce the total amount of oil entering the environment.1 Rather, they change the inherent chemical and physical properties of oil, thereby changing the oil’s transport, fate and potential effects. Small amounts of spilled oil naturally disperse into the water column, through the action of waves and other environmental processes. The objective of dispersant use is to enhance the amount of oil that physically mixes into the water column, reducing the potential that a surface slick will contaminate shoreline habitats or come into contact with birds, marine mammals, or other organisms that exist on the water surface or shoreline.  Conversely, by promoting dispersion of oil into the water column, dispersants increase the potential exposure of oil to fish and bottom dwelling biota such as clams or oysters. Dispersant application thus represents a conscious decision to increase the risk to one component of the ecosystem (e.g.,the water column) while reducing the load on another (e.g., coastal wetland). Decisions to use dispersants, therefore, involve trade-offs between decreasing the risk to water surface and shoreline habitats while increasing the potential risk to organisms in the water column and on the seafloor.

caption Aerial application of chemical diserpsant to surface oil from the Deepwater Horizon oil platform. Credit: U.S. Coast Guard.

A 2005 study by the National Research Council (NRC) on the ecological effects of dispersants concluded that there is insufficient scientific data to assess the net effect of chemical dispersants on marine and coastal ecosystems.  The NRC stated: "In many instances where a dispersed plume may come into contact with sensitive water-columns or benthic {C}{C}organisms or populations, the current understanding of key processes and mechanisms is inadequate to confidently support a decision to apply dispersants." EPA Administrator Lisa Jackson acknowledged this point in a testimony before the U.S. Senate Committe on Environment and Public Works on May 18, 2010, when she stated "...the long term effects of dispersants on aquatic life are unknown..."

During the first weeks of May, BP applied dispersant at the sea floor during EPA-sanctioned tests.  On May 7, 2010, after having deployed approximately 15,354 gallons of subsea dispersants, EPA halted subsea dispersant operations, awaiting additional test results in order to resume. Initial studies by EPA indicated that the subsurface application of approximately 10,000-15,000 gallons of dispersants have the equivalent effect on the oil as the surface application of approximately 50,000 gallons of dispersant. Thus, in principle, the subsurface application of dispersants is more efficient than surface application and could result in less dispersant being released into the environment.

On May 15, 2010, the U.S. Coast Guard and the EPA authorized BP to use dispersants undersea. Government officials stated that preliminary testing results indicate that subsea use of the dispersant is effective at reducing the amount of oil reaching the surface – and can do so with the use of less dispersant than is needed when the oil does reach the surface. Some scientists are concerned that this practice may contribute to the formation of the underwater oil plume by shaping the oil into smaller droplets. On May 17, U.S. Rep. Edward J. Markey (Massachusetts) sent a letter to EPA Administrator Lisa Jackson asking EPA to respond to concerns about the potential ecological impacts of dispersants.  

On May 19, 2010, the EPA informed BP that the company had to immediately identify and use less-toxic forms of chemical dispersants, suggesting that federal officials were concerned that the unprecedented use of chemical dispersants could pose a significant threat to the Gulf of Mexico's marine life. On May 20, 2010, the EPA began to post data from BP on the company's monitoring and sampling programs at the EPA web site.  Some of the monitoring parameters include: 1) identification of dispersed oil, 2) oil droplet size, 3) dissolved oxygen (DO) and other physical characteristics such as conductivity, temperature and depth (CTD) and, 4) toxicity information.

On May 20, 2010, BP told the EPA that it cannot find a safe, effective and available dispersant to use instead of Corexit, and will continue to use that chemical application to help break up the spill. BP told EPA that Sea-Brat 4, a proposed alternative dispersant, was rejected in part due to concern that it may degrade to a nonylphenyl, a suspected endocrine disruptor.

Some environmental scientists have criticized BP for keeping secret some of the "alternative" chemical ingredients it is using in the oil spill dispersants in its May 20 response to EPA. The EPA says BP and several of the dispersant manufacturers have claimed some sections of BP's dispersant response contain confidential business information (CBI). EPA stated that "by law, CBI cannot be immediately made public except with the company's permission," and that the "EPA is currently evaluating all legal options to ensure that the remaining redacted information is released to the public."

On May 24, 2010, the EPA directed BP to "significantly scale back the overall use of dispersants," because their data demonstrated that sub sea dispersant application was having an effect on the oil at the source of the leak, and thus far has had "no significant ecological impact." By ramping down on the amount of dispersant used, particularly on the surface where the EPA expected less un-dispersed oil because of the sub sea application, the amount of dispersant applied could be reduced by as much as half, and possibly more. By May 27, 2010, BP had reduced daily use of dispersants to 12,000 gallons from 70,000. EPA and U.S. Coast Guard continued to view BP’s scientific analysis of alternative dispersants as insufficient, stating that BP seemed " more interested in defending their initial decisions than analyzing possible better options."

On May 27, scientists that participated in a two day conference on dispersants concluded that, to date, the effects of dispersing oil into the water column has generally been less environmentally harmful than allowing the oil to migrate on the surface into the sensitive wetlands and near shore coastal habitats.  The meeting was co-sponsored by the Coastal Response Research Center at the University of New Hampshire, NOAA, EPA and the U.S. Coast Guard.

Construction of sand berms

caption Shoreline modification in coastal Louisiana to reduce oil impact on wetlands. Credit: U.S. Coast Guard.

Louisiana state officials proposed the construction of about 80 miles of sand berms along barrier islands and wetlands to capture oil from the spill. The proposed berms would run along the Chandeleur Islands chain, along federal and state wildlife refuges at the mouth of the Mississippi River, and would block oil from entering back bays and wetlands to the west of the river, all the way to the Isles Dernieres near the center of the state. The idea is that the oil would collect behind these walls of sand so cleanup crews could suck it up before it reaches the marshes.

The plan requires a permit from the U.S. Corps of Engineers and from the U.S. Coast Guard which oversees the government response. But federal officials and some scientists expressed concern about the plan.  Some experts question whether dredging companies could build up the barrier islands quickly enough to save the marshes. There is also concern that the kind of sand berms envisioned in the plan might wash away quickly after a couple of storms, wasting scarce sand in the region.  In addition, the underwater borrow pits proposed by the state could be too close to the berms, and thus could cause greater erosion to existing barrier islands or other environmental problems. Some scientists are concerned that the berms could block inlets that carry water to the wetlands on shore and interfere with the movement of organisms that depend on tidal flushing.

The feasibility and cost of the berm project is a point of contention between state and local officials. On May 23, 2010, Louisiana Attorney General Buddy Caldwell sent a letter to the U.S. Army Corps of Engineers Sunday advising them that the State of Louisiana was within its rights to rebuild barrier islands in order to combat the Gulf of Mexico oil spill if the Federal government did not do so first. Caldwell advised Lt. Gen. Robert L. Van Antwerp, commanding general of the Corps, that under the U.S. constitution the federal government does not have the legal authority to deny a state the right to conduct such emergency operations to protect its citizens and territory.

On May 27 the U.S government approved the state's proposal to build a 6-foot-high sand berm just south of Scofield Island, west of the Mississippi River, as a temporary barrier to oil from the Deepwater Horizon spill reaching wetlands in Barataria Bay. The cost of construction will be borne by either BP or the federal government. The island is one of six oil-protective sand berms proposed by the state that were granted an emergency permit  by the Army Corps of Engineers. The other five -- including two east of the Misssissippi River and three more to the west -- would have to be paid for by the state, with no guarantee that BP or the federal government would pick up their cost.  State officials criticized the delay in approval, and for the decison not to fund the construction for all six berms.

On June 1, the U.S. government BP directed BP directed BP to pay for five additional barrier island projects in addition to the one approved on May 27. BP announced that it supports that decision, and that the company will fund the estimated $360 million it will cost to construct the six sections. The six approved barriers -- four west of the Mississippi River and two to the east -- would rise 6 feet above sea level. They would be 300 feet wide at their base and 25 feet wide at their crown.

Paying for the clean up

The Oil Spill Liability Trust Fund (OSLTF), established in the Treasury, is available to pay the expenses of federal response to oil pollution under the Federal Water Pollution Control Act, and to compensate claims for oil removal costs and certain damages caused by oil pollution as authorized by the Oil Pollution Act of 1990 (OPA). The law requires that disbursements under the OSLTF be recovered from responsible parties liable under OPA when there is a discharge of oil to navigable waters. Aggressive collection efforts are consistent with the “polluter pays” public policy underlying the OPA. BP and Transocean have been named as responsible parties, although all claims are being processed centrally through BP.

The OPA requires that responsible parties pay the entire pricetag for cleaning up after spills from offshore drilling, including lost profits, destroyed property and lost tax revenue, but the statute caps their liability for economic damages at $75 million. In a letter to Homeland Security Secretary Janet Napolitano and Interior Secretary Ken Salazar on May 16, 2010, BP Chief Tony Hayward said the company believes claims related to the spill will exceed the limit.  Howard stated that "we are prepared to pay above $75 million on these claims and we will not seek reimbursement from the U.S. Government or the Oil Spill Liability Trust Fund."

Democratic legislators tried to speed a bill through Congress that would increase the liability cap for oil spills from $75 million to $10 billion.  Bill S.3305, the "Big Oil Bailout Prevention Liability Act" would have capped BP's liability at $10 billion, even if damages from the spill surpass that amount. The bill was killed on May 13, 2010 by Sen. Lisa Murkowski (R-Alaska), a key oil industry ally.

On June 9, BP said cost of the response to date is approximately $1.43 billion, including the cost of the spill response, containment, relief well drilling, grants to the Gulf states, claims paid, and federal costs.  BP said that 42,000 claims have been submitted and more than 20,000 payments already have been made, totaling over $53 million.

Transocean, the world's largest offshore drilling contractor which owned the Deepwater Horizon, filed papers in a Houston court on May 20, 2010, seeking to limit its legal liability to $27 million.

On June 18, Anadarko Petroleum Corporation, a 25% owner of the Gulf drilling operation in which BP owns 65%, blamed the entire disaster on the British oil company. Andarko claimed that, under an exception to a joint operating agreement’s cost and liability sharing provisions, BP was “grossly negligent” or engaged in “willful misconduct” as operator. BP reacted to the statement by saying it strongly disagreed with the Anadarko contention that all of the spill liability belonged to it.

Ecological concerns

The negative effects of oil on organisms and ecosystems are well-documented. Oil causes harm to wildlife through physical contact, ingestion, inhalation and absorption.  Floating oil can contaminate plankton, which includes algae, fish eggs, and the larvae of various invertebrates. Long term damage to lower trophic levels is difficult to assess, but could pose ecological risks in the Gulf of Mexico for years, based upon interference with metabolic functions of thousands of species; benthic organisms in the inner and outer continental shelves could be affected from oil coating of substantial portions of the ocean floor. Birds can be exposed to oil as they float on the water or dive for fish through oil-slicked water. Oiled birds can lose the ability to fly and can ingest the oil while preening. Sea turtles such as loggerheads and leatherbacks can be impacted as they swim to shore for nesting activities. Turtle nest eggs may be damaged if an oiled adult lies on the nest. Scavengers such as bald eagles, gulls, raccoons, and skunks are also exposed to oil by feeding on carcasses of contaminated fish and wildlife. 

caption A sea turtle covered in oil from the Deepwater Horizon site. Credit: Louisiana Fish and Wildlife.

Oil has the potential to persist in the environment long after a spill and have long-term impacts on fish and wildlife, interacting with the environment. Long-term effects on birds and marine mammals are less understood, but oil ingestion has been shown to cause suppression to the immune system, organ damage, behavioral changes, skin irritation and ulceration.

The area affected by the Deepwater Horizon oil spill has some of the world's most productive marine and coastal ecosystems. Southern Louisiana has about 40% of the nation's coastal wetlands.  These wetlands provide a range of goods and services, including flood control, water purification, storm buffer, wildlife habitat, nursery grounds for aquatic life, and recreational areas. Louisiana wetlands have been heavily degraded by human activity. In particular, marsh has been lost--converted to open water--for decades due to oil and gas development, dredging and levee construction for navigation and flood control, and other human disturbance. Louisiana has lost 1,900 square miles of land since the 1930's.  Between 1990 and 2000, wetland loss was approximately 24 square miles per year- that is the equivalent of approximately one football field lost every 38 minutes. Degradation by oil of the marsh grass, that is essential for holding sediment in place, could accelerate wetland loss.

The location of the spill site is in the ocean zone known as the Bathypelagic, a depth which has pressure as great as 160 atmospheres and temperatures of merely a few degrees Celsius. This depth is almost devoid of sunlight and hence offers virtually no primary production, but there are a variety of bioluminescent and soft muscled creatures, many of which we know little about. Due to pelagic mixing, the crude oil will migrate vertically and affect all depths of the waters of the Gulf of Mexico, including the shallower waters, where substantially more biodiversity and biological productivity is present.

Scientists at Texas A&M University-Corpus Christi recently completed a comprehensive survey of the Gulf's biodiversity. They found that that the NNE octant of the Gulf (that area containing the Deepwater Horizon site) contains 8,332 species of plants and animals. Including only the major taxa of animals at all depths in the region of the spill, there are 1,461 mollusks, 604 polychaetes, 1503 crustaceans, 1,270 fishes, 4 sea turtles, 218 birds and 29 marine mammal species.

Scientist's familiar with the Gulf of Mexico cite a number of concerns about the timing of the spill:

  • Breeding Season: Invertebrates, sea turtles, and birds will be facing the brunt of the spill just as they are laying eggs or caring for them in important wildlife areas.  Scientists say that it is virtually certain that billions of fish eggs and larvae died in the spill because the spawning season for many fish in the Gulf begins in April and runs into the summer.
  • Trans-Gulf Migration Season: Tens of millions of birds cross the Gulf of Mexico from the Yucatan Peninsula and South America to the U. S. Gulf Coast (Texas to Florida). The spill occurred near the peak of the Trans-Gulf Migration Season.
  • Hurricane Season: A big storm could complicate recovery and cleanup efforts and spread oil throughout the
    Gulf. The first of June is the official start of hurricane season.  NOAA and others are predicting a particularly rough year for Atlantic storms.
  • La Niña: Moderate El Niño conditions are expected to dissipate by June. That phenomenon, which means warmer Pacific waters, creates so-called wind shear in the Atlantic that helps break up hurricanes as they form. So without El Niño, June storms might be more likely to form. In its place, say several climate models, is a La Niña period, which means warmer temperatures in the southern areas of the United States and generally more powerful storms.

The U.S. Fish and Wildlife Service identified 32 National Wildlife Refuges at risk from the Deepwater Horizon oil spill that line the coasts of Louisiana, Mississippi, Alabama and Florida. Of particular concern are Refuges in the Southeast Louisiana (SELA) Refuges Complex, including Breton National Wildlife Refuge, the second oldest refuge in the country. The coastal wetlands in this complex support some of the nation's most abundant wildlife, including nesting wading birds and seabirds, passerine birds (songbirds), raptors, as well as wintering shorebirds and waterfowl. For example, coastal wetlands are relied on by all 110 neo-tropical migratory songbird species— as many as 25 million can pass through the area each day during the breeding season.

The wetlands in the Refuges and other coastal regions also support a diversity of fish and shellfish species, including Speckled trout, redfish, flounder, blue crabs and shrimp.  These coastal wetlands are extremely important nursery areas for both fresh and saltwater fish species. Endangered and threatened species at risk from the spill include West Indian manatees, whooping cranes, Mississippi sand hill cranes, wood storks and four species of sea turtles.

Widespread impacts on wildlife were observed beginning the week of May 16.  By May 24, 2010 two rookeries for brown pelicans in Barataria Bay showed signs that oil had breached the protective booms. By the first week of June, reports of death and injury to birds, sea turtles and dophins were rising sharply across the Louisiana coast.

The possible impacts of crude oil and chemical dispersants in the open waters of the Gulf of Mexico are largely unknown and extremely difficult to assess. Another area of concern is the Pinnacles Region, an extensive deep (~100 m) reef tract on the Mississippi-Alabama outer continental shelf (OCS). Most of these formations are fossil reefs that are no longer actively accreting, and do not support true reef-building algae or corals. They nonetheless support a well-developed community of reef-dependent and reef-associated organisms and a relatively diverse population of fish and fauna when compared to surrounding soft sediments.

On May 2, 2010, BP announced commitment of up to $500 million to an "open research program" studying the impact of the Deepwater Horizon spill, and its associated response, on the marine and shoreline environment of the Gulf of Mexico. BP stated that it will appoint an independent advisory panel to construct the long term research program.

In the weeks after the accident, coastal and marine scientists from Texas to the Everglades collected soil and water samples as well as tissue from mollusks and coastal marine life that could be affected if the effects of the spill spread. This information will provide the baseline data needed to assess any impacts that do occur.

Another area of concern is the effect of oil on so called cold "seep communities", areas of the ocean floor that are rich in hydrogen sulfide, methane and other hydrocarbon-rich fluids released through natural seeps. These unique systems rely on chemosynthetic organisms that derive their energy from chemosynthesis rather than photosynthesis. Clams, mussels, corals and tube worms that are centuries old live in the cold seeps. The systems are abated the low, diffuse, chronic seepage of petrochemicals that is common in the norther Gulf of Mexico. What is not known is how these organisms will respond to the concentrated surge oil that they may be exposed to from the Deepwater Horizon site.

Fish and Wildlife Collection Report

caption An oiled pelican in coastal Louisiana. Credit: Carolyn Cole, Los Angeles Times.

On May 30, 2010, the Unified Area Command published its first "Consolidated Fish and Wildlife Collection Report." These are the consolidated numbers of collected fish and wildlife that have been reported to the Unified Area Command from the U.S. Fish and Wildlife Service (USFWS), National Oceanic and Atmospheric Administration (NOAA), incident area commands, rehabilitation centers and other authorized sources operating within the Deepwater Horizon/BP incident impact area. These data reflect only the initial, field-level, evaluation and they do not reflect a final determination of the cause of injury, or death. Not all of the injured or dead fish and wildlife reflected in these numbers were necessarily caused by the Deepwater Horizon/BP incident. On the June 16 the report included:

Birds: 1,746 birds collected, with 1,014 of these visibly oiled. 997 birds were dead; 749 were captured alive.

Sea Turtles: 528 collected; 400 were dead; 128 were alive.

Mammals, Including Dolphins: 51 collected in the spill zone; 47 of those were dead. Determination whether oil was the cause of death is pending for dolphins.

Wildlife biologists believe that many more wildlife will ultimately be killed by the oil, but their toll is hidden because their bodies have sunk in the open ocean, or been eaten by scavengers.

By way of comparison, the Exxon Valdez oil spill killed between 350,000 and 600,000 birds, along with thousands of sea otters and other marine creatures.

Antecedent events

Several events leading up to the Deepwater Horizon oil spill may be germane in understanding the context of this incident. These matters include trends in deepwater drilling in the Gulf of Mexico; permit processing; and preparedness steps.

The Wall Street Journal reports that in the year 2009, deepwater drilling in the Gulf of Mexico increased over 2008 (and the average for the previous ten years) by fifty percent, or a jump of 150 million barrels per annum of crude oil. The New York Times on May 13 reported that over 300 offshore drilling permits had been issued by the U.S. government without proper approval by NOAA in the prior year to the incident. The New York Times elaborated: "Federal records indicate that these consultations ended with NOAA instructing the minerals agency that continued drilling in the gulf was harming endangered marine mammals and that the agency needed to get permits to be in compliance with federal law."

Exclusion from environmental review

During the Bush Administration in 2004, the MMS granted a “categorical exclusion” from the National Environmental Policy Act (NEPA) to certain oil and gas activities in the Gulf of Mexico, including individual exploration plans. The MMS essentially said that it will not thoroughly review the environmental impacts of certain activities, including such activities as the exploration phase for the Deepwater Horizon site. Some legal analysts argue that this was wrong because the 2004 MMS Departmental Manual explicitly stated that a categorical exclusion should not be issued if the lease or exploration is: (1) In areas of high seismic risk or seismicity, relatively untested deepwater, or remote areas; or (2) Within the boundary of a proposed or established marine sanctuary, and/or within or near the boundary of a proposed or established wildlife refuge or areas of high biological sensitivity; or (3) In areas of hazardous natural bottom conditions; or (4) Utilizing new or unusual technology. The Deepwater Horizon project was deep and it used new technology.

Mark Chernaik at the Environmental Law Alliance Worldwide notes that the Draft Environmental Impact Statement (DEIS) for a cluster of 11 oil and gas lease sales that included Oil and Gas Lease Sale 206, the site of the Deepwater Horizon rig explosion and oil spill was seriously flawed. Prepared by the Minerals Management Service, the DEIS never assessed the impact of a catastrophic spill, limiting its focus to spills no larger than 4,600 barrels. The DEIS also failed to propose the use of one safeguard — an acoustic control system for blowout prevention — that might have promptly contained the spill when the manual blowout preventers failed. Such systems are required in some countries, but they were not even proposed in the DEIS.  BP's 52 page exploration and environmental impact plan for the Deepwater Horizon well stated that it was "unlikely that an accidental surface or subsurface oil spill would occur from the proposed activities" and that "due to the distance to shore (48 miles) and the response capabilities that would be implemented, no significant adverse impacts are expected."

Early in 2009, BP sought approval of the exploration plan for this well, whose flaws might have been detected by a full blown review under NEPA.  That did not occur due to the categorical exclusion, so when the MMS approved the exploration plan for this well on April 6, 2009, it did so in compliance with the 2004 policy decision to limit environmental review of oil and gas activities in the Gulf.

The MMS' own environmental assessements downplayed the potential for environmental damage. In a 2007 environmental impact statement for the Western and Central Planning Area Sales, which covered oil drilling leases from 2007-2012 for the region that included the Macondo Prospect where the Deepwater Horizon operated, the MMS assessed the potential impact of oil spills and blowouts on wetlands, marine mammals, commercial fishing, economic impacts, and water quality.  MMS stated:

  • "Offshore oil spills resulting from a proposed action are not expected to damage significantly any wetlands along the Gulf Coast... Overall, impacts to wetland habitats from an oil spill associated with activities related to a proposed action would be expected to be low and temporary."
  • "At the expected level of impact, the resultant influence on commercial fishing activities from a proposed action would be negligible and indistinguishable from variations due to natural causes."
  • "Since LWC [loss of well control] events and blowouts are rare events and of short duration, potential impacts to marine water quality are not expected to be significant."

On May 17, 2010, the Defenders of Wildlife and the Southern Environmental Law Center filed suit against the Minerals Management Service’s (MMS) for "lax oversight of oil drilling operations, including its failure to require a thorough examination of spill risks from exploratory drilling operations like the Deepwater Horizon." The suit seeks to prohibit the MMS from continuing to exempt from environmental review new exploratory drilling operations in the Gulf of Mexico. The suit argues that the MMS’ continued exemption of over 20 new structures and exploratory wells—including four at almost twice the depth (over 9,000 feet) of the Deepwater Horizon (almost 5,000 feet)—from environmental review of the risks after the current oil spill is a violation of the National Environmental Policy Act.

Questions about Blowout Preventers

The Deepwater Horizon blowout preventer (BOP) was not equipped with a remote control shut-off failsafe switch required in two other major oil-producing nations as last-resort protection against underwater spills. Both Norway and Brazil require such a device, which costs about $500,000. U.S. Federal regulators had specifically exempted the Deepwater Horizon from having such a remote shut-off switch partially on the grounds of the costliness of the device (less than one percent of the Deepwater Horizon capital cost).

The failure of the BOP was foreshadowed by a 2003 paper by Deepwater Horizon owner Transocean that highlighted problems with hydraulic components of BOP control systems across the industry and suggested equipment was being rushed into the field with limited testing. Other studies had noted that a part of the BOP called a shear ram —the last line of defense that is intended to cut and close a drill pipe when all else fails — can't always slice through the thick pipe used in deepwater drilling. A 2004 study commissioned by federal regulators found that only three of 14 newly built rigs had shears powerful enough to cut through pipe at the equipment's maximum water depth.

In 2001, the U.S. Minerals Management Service proposed rules that would have required emergency backup control systems on BOP systems. The proposed rules were not yet law at the time of the Deepwater Horizon accident.

Questions About Cementing

An Associated Press report published on May 24, 2010 suggested that lax federal regulation oil well cementing--a suspected cause of the accident--contributed to the disaster. Federal regulators don't regulate what type of cement is used, leaving it up to oil and gas companies, who are "urged" to simply follow guidelines of the American Petroleum Institute, an industry trade group. Far more stringent federal and state standards and controls exist on cement work for roads, bridges and buildings. Reports by the MMS named cementing as a factor in 18 of 39 well blowouts at Gulf rigs from 1992 to 2006, and five of nine out-of-control wells in the year 2000 were related to cementing problems.

Government response

Timeline of key actions

The Coast Guard responded to the explosion and fire on April 20, 2010, treating the event as a Search and Rescue (SAR) operation. The next day, on April 21, 2010, the Coast Guard continued its search for the missing eleven people.

caption A boom on the Louisiana coast collecting oil from the Deepwater Horizon accident. Credit: Louisiana Fish and Wildlife.

Concurrent with the SAR, efforts began to assess the containment of the oil release. The federal government's response to such an event so governed by the National Contingency Plan (NCP) a blueprint for responding to both oil spills and hazardous substance releases. Pursuant to the NCP, the Administration named Rear Admiral Mary Landry the Federal On-Scene Coordinator. A Regional Response Team was established, including representatives of the Coast Guard, Department of Homeland Security (DHS), Department of Commerce (DOC)/NOAA, Department of the Interior (DOI) and the EPA, as well as state and local representatives.

In the weeks following the spill, a number of government probes were announced into the Deepwater Horizon explosion and oil spill. These included probes by the Marine Board of Investigation (Coast Guard and Minerals Management Service), Interior Department Outer Continental Shelf Safety Board, National Academy of Engineering, House Energy and Commerce Committee, House Oversight and Government Reform Committee, and House Natural Resources Committee.

On April 22, 2010, a National Response Team (NRT), an organization of 16 federal departments and agencies responsible for coordinating emergency preparedness and response to oil and hazardous substance pollution events, convened its first daily meeting with leadership from across the federal government. Participants in the meeting included the White House, U.S. Coast Guard, the Department of Defense, DHS, DOC, DOI and EPA, among others.

On April 23, 2010, the Unified Area Command was formally stood up in Robert, La., after three days of informal operations and planning. The U.S. Coast Guard announced that the Deepwater Horizon rig had been found upside down approximately 1,500 feet northwest of the blowout preventer at the wellhead. At 5 p.m., the Coast Guard suspended the search for the 11 missing workers.

On April 29, 2010, Department of Homeland Security Secretary Janet Napolitano declared the event a Spill of National Significance (SONS), indicating that the government would designate more forces to contain the spill.  This designation also led to the naming of U.S. Coast Guard Commandant Admiral Thad Allen as the National Incident Commander on May 1, 2010, which provided additional authority and oversight in leveraging government assets to combat the spill.

The Council on Environmental Quality and the Department of the Interior announced a review of the National Environmental Policy Act procedures for the Minerals Management Service (MMS), the bureau in DOI that manages the nation’s natural gas, oil and other mineral resources on the outer continental shelf (OCS). The review will examine the MMS NEPA procedures for OCS oil and gas exploration and development.

On May 17, 2010, the Small Business Administration deployed staff to Louisiana, Mississippi, Alabama and Florida to meet individually with business owners, answer questions about the Economic Injury Disaster Loan program, issue loan applications, and provide help in completing the loan forms via business outreach centers.

On May 21, 2010, President Barack Obama issued an Executive Order that created the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling. The Commission will be chaired by former two-term Florida Governor and former Senator Bob Graham and former Administrator of the Environmental Protection Agency William K. Reilly. The seven member commission was intended to be bipartisan with "broad and diverse representation of individuals with relevant expertise." No currently serving government employees or elected officials will sit on the commission.

On June 1, 2010, Attorney General Eric H. Holder Jr. announced that the Justice Department had begun civil and criminal investigations. Holder said  they were reviewing violations of the Clean Water Act, which carries criminal and civil penalties and fines; the Oil Pollution Act of 1990, which can be used to hold parties responsible for cleanup costs; the Migratory Bird Treaty Act and the Endangered Species Act, which provide penalties for injury and death of wildlife.

On June 8, 2010, the Department of the Interior issued a directive to oil and gas lessees and operators on the Outer Continental Shelf implementing seven stronger stronger safety requirements. The new requirements focused on greater independent review and verification of safe operating procedures for offshore drilling.

On June 8, 2010, the Department of Energy started online access to schematics, pressure tests, diagnostic results and other data about the malfunctioning blowout preventer. There is also a timeline of key events and detailed summaries of the Deepwater well configuration, the blowout preventer stack tubes, and the containment system.

On June 15, 2010, President Barack Obama gave an an 18-minute speech from the Oval Office about the oil spill that was carried in prime time by many TV networks.

On June 16, 2010, BP agreed to create an independent $20 billion fund to pay claims arising from the oil spill. The company also said it would suspend paying dividends to its shareholders for the rest of the year and would compensate oil field workers for lost wages. The fund will be run by Kenneth R. Feinberg, the mediator who oversaw the compensation fund for the victims of the Sept. 11 attacks.

Drilling moratorium

On May 27, President Barack Obama rescinded his March 31, 2010 proposal for expanded offshore drilling, and instituted a temporary halt to drilling and new safety requirements. Key details of the moratorium and licensing changes include:

  • No new drilling will be allowed in water depths greater than 500 feet for six months, including sidetracks and bypasses of currently-drilling wells.
  • Drilling on 33 wells will be suspended at the first safe stopping point.
  • Workover activities, well completions, abandonment activities, interventions, and waterflood, gas injection, and disposal wells will not be affected.
  • Drilling offshore Alaska will be postponed until at least 2011.
  • Western GoM Lease Sale 215 and the proposed Virginia Lease Sale 220 have been cancelled.
  • The three other remaining GoM lease sales in the 2007 – 2012 OCS Leasing Program are subject to review.
  • New standards for equipment and procedures will be implemented, with a focus on blowout preventers (BOPs), well control systems (fluid displacement procedures), casing and cementing.
caption The Nansen production platform operates in about 3,500 feet of water off the Texas coast. Credit: Devon Energy.

On May 28, 2010, Interior Secretary Salazar issued a memorandum to the Director of the MMS that directed the MMS to not process any new applications for permits to drill consistent with that directive. Confusion arose in the following week regarding whether the moratorium covered all wells, or just "deep" wells. A regional office of the MMS issued two drilling permits for shallow wells off the coasts Louisiana and Mississipi on June 2, but the permits were rescinded on June 3.  An Interior spokeswoman said that the MMS rescinded the permits "out of caution" and "to ensure that new drilling activities are consistent with" new federal safety requirements.

The oil industry was highly critical of the drilling moratorium. The American Petroleum Institute, an industry trade group, stated that an extended moratorium "would create a moratorium on economic growth and job creation--especially in the Gulf States whose people and economies have already been most affected by the oil spill--by undercutting our nation's access to affordable, reliable, domestic sources of oil and natural gas." The Louisiana Mid-Continent Oil and Gas Association estimated that the idle drilling rigs would reduce commerce by $16.5 million per day, and that wages lost lost by those who work on the idled drilling platforms could reach as high as $330 million per month.

The moratorium was also criticized by members of a panel of experts identified by the National Academy of Engineering who had been asked to review a draft of Secretary Salzar's report on measures to improve offshore safety. The final version delivered to President Obama on May 27 included the drilling moratorium, but angry panel members and some others who contributed to the Salazar report said they had reviewed only an earlier version of the secretary's report that suggested a six-month moratorium only on new drilling, and then only in waters deeper than 1,000 feet. "We broadly agree with the detailed recommendations in the report and compliment the Department of Interior for its efforts," a joint letter from the panelists to various politicians says. "However, we do not agree with the six month blanket moratorium on floating drilling. A moratorium was added after the final review and was never agreed to by the contributors."

New rules issued on June 8, 2010 by the Interior Department tightened standards for barriers at underwater wells and blowout preventers. The new rules also shifted the cost and accountability of verification, certification and inspection from the government directly to the leaseholder by requiring safety inspections by professional engineers and other independent analysts — rather than having Interior Department investigators sign off on well plans and equipment. The new rules required that CEOs must certify, under penalty of criminal prosecution, that their operations comply with all regulations, equipment has been tested and all personnel are trained.  Drilling operations were allowed to resume in less than 500 feet below the surface of the sea once the new standards were met; the drilling ban remained in effect for sites in deeper water.

On June 22, 2010, a judge in United States District Court in New Orleans issued a preliminary injunction against the enforcement of the moratorium, citing potential economic harm to businesses and workers. The Court concluded that wrote that the Obama administration had failed to justify the need for such “a blanket, generic, indeed punitive, moratorium” on deep water drilling. The White House said it “will immediately appeal” the judge’s ruling to a federal appeals court in New Orleans. Interior Secretary Salazar said he would issue a new order that would contain additional information showing why it was necessary.

The Obama Deepwater Horizon Oil Spill Legislative Package

caption Oil-soaked hands of a worker from the Deepwater Horizon clean-up. Credit: U.S. Coast Guard.

President Barack Obama sent a legislative package to Congress on May 12 whose purpose was to "continue expeditiously, speed assistance to people affected by this spill, and strengthen and update the oil spill liability system to better address catastrophic events." The package proposed funding for small business loans, oil spill unemployment assistance, nutrition assistance, disaster relief for fishermen and communities, and grants to state and local communities. The President's plan would fund the U.S. Food and Drug Administration to monitor and respond to the environmental impact of the oil on seafood fished from the gulf and surrounding areas. It also increased funding to the Secretary of the Interior for additional inspections, enforcement, studies and other activities that are outside of those recoverable from the responsible parties or the Oil Spill Liability Trust Fund. The bill would extend the time allowed by statute for the Minerals Management Service to review and approve oil and gas lessee exploration plans to allow additional time for the required review. The legislation would also provide funding to the EPA and NOAA for various environmental studies that improve the federal response to the spill.

The Obama bill would raise the statutory expenditure limitation for the Oil Spill Liability Trust Fund from $1 billion to $1.5 billion and the cap on natural resource damage assessments and claims from $500 million to $750 million. The proposal would also raise the caps on liability for responsible parties, and increase the tax that oil companies pay to finance the Oil Spill Liability Trust Fund from 8 cents per barrel (per 42 gallons) to 9 cents per barrel starting this year.

Problems in the Minerals Management Service

In the wake of theDeepwater Horizon accident, the Minerals Management Service came under heavy criticism for alleged conflicts of interest among its competing missions. The agency was tasked with collecting royalties from oil and gas produced on federal lands and issuing energy leases; at the same time it also is responsible for policing offshore drilling and setting regulations for the industry. Indeed, in the wake of the spill President Barack Obama noted a "cozy relationship" between federal regulators at the MMS and the industry they police. Investigations revealed, for example, that some employees at the minerals service accepted lavish gifts from oil companies and allowed companies to fill out their own inspection reports. Other MMS employees lobbied for jobs at the companies they were supposed to regulate. Minerals Management Service officials can receive cash bonuses in the thousands of dollars based in large part on meeting federal deadlines for leasing offshore oil and gas exploration

MMS regulators repeatedly ignored warnings from government scientists about environmental risks in its push to approve energy exploration activities quickly. In a 2009 response to MMS' proposed five-year plan for oil and gas leasing, the National Oceanic and Atmospheric Administration (NOAA) said that MMS understated the scale of oil spills. NOAA concluded that MMS some statements "seem to directly conflict with studies of major spills," and that the MMS did not fully evaluate oil spill modeling.

According to a report by theWashington Post, a review panel with NOAA issued a scathing critique of Shell Exploration and Production's plan to conduct an open-water marine survey in Alaska's Chukchi Sea, finding "... no clearly stated 'scientific objectives.' " The Post report described "a war between the biologists and the engineers" in which MMS regulators frequently changed documents and bypassed legal requirements aimed at protecting the marine environment.

Several government watchdog groups have criticized the "revolving door" through which drilling regulators move from government to industry and back again, sometimes on multiple occasions. The Associated Press reported that one MMS employee who was critical of industry drilling regulations in 2005, later became an employee of BP and argued against more stringent environmental regulation of the industry.

On May 19, 2010, Interior Secretary Ken Salazar announced a plan for breaking the MMS into three separate bureaus:

  • The Bureau of Ocean Energy Management, which would be responsible for development of conventional and renewable energy resources on the outer continental shelf.
  • The Office of Natural Resources Revenue, which would be responsible for collecting and distributing royalties from oil and gas produced on federal lands and waters.
  • The Bureau of Safety and Environmental Enforcement, which would be tasked with broadly overseeing energy production and imposing safety and environmental regulations on all offshore energy activities.

On May 27, 2010, Elizabeth Birnbaum, the director of the U.S. Minerals Management Service, resigned.  Interior Secretary Ken Salazar praised Birnbaum as "a strong and effective person and leader" and said she "resigned today on her own terms and on her own volition," but White House officials made clear that Birnbaum had been forced out. On May 28, 2010, Bureau of Land Management Director Bob Abbey was named as acting director of the MMS.

Criticism of the Administration Response

A month after the accident, the Obama administration came under increasingly sharp criticism for underestimating the size of the discharge, for the lack of transparency in its response efforts, and for being too easy on BP and the oil industry. Scientists have been especially critical of the Administration for not forcing BP to fund and make publicly available more data from subsurface analysis of the leak, aerial surveillance of the ocean surface, the extent and impact of the subsurface oil plume, and the fate and impact of chemical dispersants. Scientists criticized the EPA for not releasing its finds from offshore water sampling, and they questioned why NOAA was so slow to investigate the magnitude of the spill and the damage it is causing.

Government critics point out that BP also has ties to the Department of Energy. Steven Chu was the head of Lawrence Berkeley National Laboratory at the University of California, Berkeley, when the Lab received the bulk of a $500 million grant from the British oil giant BP to develop alternative energy sources through a new Energy Biosciences Institute. Dr. Chu received the grant from BP’s chief scientist at the time, Steven E. Koonin. Dr. Chu is now the Secretary of the Department of Energy, and Dr. Koonin, who followed Dr. Chu to the Energy Department, now serves as under secretary of energy for science. No one has accused Dr. Chu or Dr. Koonin of direct conflict of interest or questioned their scientific credentials, and the Department of Energy has no direct responsibility for the cleanup. Dr. Koonin is recused from all matters relating to the disaster because of his past ties to BP.

The Response by Congress

caption Oil industry executives testifying before Congress about the Deepwater Horizon accident

Main article: Congressional hearings on the Deepwater Horizon oil spill

The U.S. Congress reacted swiftly to the accident, holding nine hearings and three briefings on the oil spill in the first few weeks, with many more planned.  A month after the accident, 10 different House and Senate committees were probing the Deepwater Horizon disaster. The hearings were part political theater, but they also produced important breakthroughs in the investigation.  For example, Reps. Henry Waxman, D-Calif., and Bart Stupak, D-Mich., used their leadership roles on the House Energy and Commerce Committee to persuade BP and Transocean to turn over timelines and test data from the damaged well. Rep. Ed Markey, D-Mass., used his committee chairmanship to successfully pressure BP to release live video of the leak. Hearings in the House also helped pressure EPA to force BP to investigate alternatives to its choice of dispersants to break up the oil

BP's internal investigation

Main Article: BP's Deepwater Horizon accident investigation report

On September 8, 2010, BP published its internal investigation team's report into the accident. The inquiry was led by the company’s safety chief, Mark Bly, and a team of about 50 made up mostly of BP employees. The 234 page report identified eight critical factors that led to the accident, including weaknesses in the cement, design and testing of the well; misreading of pressure tests even though the well was not completely sealed; and the failure of the blow-out preventer – valves to stop gas and oil escaping – to operate. One key finding was that rather than traveling up a narrow channel outside the well’s interior pipe casing, volatile gas likely entered the casing itself through a series of barriers at the bottom of the well called a shoe track.

The report assigns partial blame to BP in just two of the eight factors leading to the explosion. The report repeatedly points to the failure of cement barriers in the well, a focus that shifts attention to the work done by the cement contractor Halliburton Co. In particular, the report alleged that Halliburton failed to conduct adequate testing of the specific cement slurry used at the well. The reports also pinned responsibility on the rig's owner, stating that:

"Transocean was solely responsible for operation of the drilling rig and for operations safety. It was required to maintain well control equipment and use all reasonable means to control and prevent fire and blowouts."

In response, Transocean dismissed the BP report as a “self-serving report ... that attempted to conceal the critical factor that set the stage for the Macondo [well] incident: BP’s fatally flawed well design. In both its design and construction, BP made a series of cost-saving decisions that increased risk – in some cases, severely.” Halliburton pointed to a number of “substantial omissions and inaccuracies”.

Other analysts observed that BP drew their conclusions without interviews of all involved or even inspecting the rig, which was still on the bottom, as well as the lack of available evidence. BP did not investigate organizational issues and rig scheduling, which could have caused worker fatigue, contributing to the confusion prior to the well blowout.

Skeptics argued that the report amounted to a preview of BP's legal defense. If BP is found to have been grossly negligent in its role as operator, the fines it faces would increase by billions of dollars and its chances of recouping money from its junior partners in the project, Anadarko and Mitsui, would be reduced.

Economic Impacts

caption Shrimp harvest in Louisiana. Credit: Louisiana Fish and Wildlife.

The economic impacts from the spill originate in the communities affected by the spill, but then ripple throughout the entire nation. Commercial fishermen in the Gulf harvested more than 1 billion pounds of fish and shellfish in 2008. In addition, there are approximately 5.7 million recreational fishermen in the Gulf of Mexico region who took 25 million fishing trips in 2008. Fisherman in areas closed to fishing, or whose catch are harmed by the spill, feel the immediate effects, as do hotels, restaurants and other businesses that are tied to tourism, conventions and recreation in the Gulf Coast. The reduction in the harvest of oysters, shrimp and other seafood caused prices to rise sharply in the weeks following the spill, which in turn caused food prices to rise in restaurants as far away as New York City. The mere threat of oil caused thousands of hotel cancellations in the run-up to the usually hectic Memorial Day weekend.

Florida's Department of Tourism tried to alleviate public concern about its beaches by posting information about Florida’s destinations on its Web site in real time with beach Webcams, Twitter feeds and photos. Gov. Charlie Crist said he had secured $25 million from BP to finance the tourism advertising campaign after an initial $25 million went to disaster preparation and response.

On May 24, 2010, U.S. Commerce Secretary Gary Locke declared a "fishery disaster" in the Gulf of Mexico due to the economic impact on commercial and recreational fisheries from the Deepwater Horizon accident. The affected area includes the states of Louisiana, Mississippi and Alabama. The declaration makes it easier to mobilize federal relief efforts.

The oil spill clean-up also generates economic benefits. Cleanup crews and reporters covering the spill have replaced oil field workers and fishermen in some hotels and restaurants, and some fishermen could use their boats in spill clean up. Companies that specialize in booms, chemical dispersant, hazardous materials training and other spill-related services experienced a significant boom in business.

In a preliminary assessment of the economic dmamage released on May 17, 2010, Moody's Investors Service suggested that while Louisiana, Mississippi and Alabama may experience short-term economic booms related to clean-up efforts, that will give way to longer term deteriorating revenue for coastal communities. Cities and counties in those Gulf states are likely to experience a decline in property tax values, which will mean a reduction in services or a necessary increase in revenue to maintain current credit rating levels. The long-term economic and financial impact on those states may be manageable, however, especially since there is a short-term economic boom and BP has pledged to pay cleanup costs and damage claims, Moody's said. But it's likely there will be a more severe impact on communities in Florida, which is highly dependent on tourism and sales tax.

The Department of Energy announced that its national laboratories were working with the Department of Homeland Security's National Infrastructure Simulation and Analysis Center (NISAC), which is modeling the economic costs and societal impact of the oil spill on energy and other industries in the Gulf and along the coast to support the response efforts of the National Incident Commander and the Unified Area Command. NISAC is a modeling, simulation, and analysis center within DHS that leverages national expertise to address infrastructure protection.

The Deepwater Horizon disaster is widely expected to send insurance costs higher for deepwater drilling.

On June 1, 2010, led by a drop in energy stocks, the Dow Jones industrial average fell 120 points shortly after the Obama Administration announced its criminal investigation into the disaster. BP lost 15 percent of its market value during the day’s trading. Fearful that the spill could ultimately cost BP tens of billions of dollars, by June 15 investors have driven the company’s market valuation down by 48 percent since the spill began, erasing $91 billion of shareholder value.

On June 8, 2010, Sean Snaith, an economist at the University of Central Florida, said that a worst case scenario--i.e., Florida beaches suffer a massive, direct hit from the Gulf oil spill--could cost $10 billion and put about 195,000 people out of work.

BP environmental and safety record

Exxon Valdez oil spill

caption Cleanup in Prince William Sound, Alaska, after the Exxon Valdez accident in 1989.

BP was heavily criticized for its role in the response to the Exxon Valdez oil spill in Alaska in 1989, one of the largest in the nation's history.  BP owned a controlling interest in Alyeska, the Alaska oil industry consortium that was responsible for designing, constructing, operating, and maintaining the Trans Alaska Pipeline System (TAPS). The pipeline stretches from the Arctic Ocean to the Valdez terminal on the Pacific. Alyeska was required to write the Oil Spill Response Plan (OSRP), and to respond to the spill. The Alaska Oil Spill Commission's report dedicated an entire chapter to failures by Alyeska, who essentially ran the first days of containment efforts in Prince William Sound, an inlet on the south coast of Alaska. The Commission found that Aleyska failed to make good on its own plan in numerous ways: slow response, and an overall lack of skimmers, barges to store captured oil, helicopters, and crews on standby.

California oil refineries

A ProPublica study reported that in 2002, California officials discovered that BP had falsified inspections of fuel tanks at a Los Angeles-area refinery and that more than 80 percent of the facilities didn't meet requirements to maintain storage tanks without leaks or damage. Inspectors were forced to get a warrant before BP allowed them to check the tanks. The company eventually settled a civil lawsuit brought by the South Coast Air Quality Management District for more than $100 million.

Texas City refinery disaster

caption The BP Texas City refinery after the explosion and fire in 2005. Credit: AP.

The BP Texas City Refinery suffered one of the worst industrial disasters in recent U.S. history. Explosions and fires killed 15 people and injured another 180, and resulted in financial losses exceeding $1.5 billion. According to the U.S. Chemical Safety Board, the Texas City disaster was caused by organizational and safety deficiencies at all levels of the BP Corporation. Warning signs of a possible disaster were present for several years, but company officials did not intervene effectively to prevent it.

After the disaster, BP agreed to pay out $1.6 billion in private settlements and then plead guilty to lesser criminal violations. BP Products North America agreed in 2007 to plead guilty to a felony for failing to have adequate written procedures and for failing to inform contractors of the hazards related to their occupancy of temporary trailers located near the refinery’s isomerization unit. BP Products agreed to a $50 million fine and three years probation. In 2009, the Occupational Safety and Health Administration on Friday imposed an $87 million fine against BP for failing to correct safety hazards after the 2005 disaster. The fine - at the time the largest in OSHA's history - came after a 6-month inspection revealed hundreds of violations of the settlement agreement to repair hazards at the refinery.

Prudhoe Bay oil spill

caption Workers clean up an oil spill from a BP oil pipeline near Prudhoe Bay, Alaska in 2006. Credit: Blooomberg

On October 25, 2007, the British Petroleum Exploration (Alaska ), Inc., (BPXA) agreed to plead guilty to a criminal violation of the Clean Water Act to resolve its criminal liability relating to pipeline leaks of crude oil onto the tundra and a frozen lake in Alaska. The first pipeline leak, discovered on March 2, 2006, resulted in more than 200,000 gallons of crude oil spreading over the tundra and a nearby frozen lake. This was the largest spill ever to occur on the North Slope. The second leak occurred in August of 2006, but was quickly discovered and contained after leaking approximately 1,000 gallons of oil onto the tundra.  As part of the guilty plea BPXA agreed to a total of $20 Million of which $12 million is criminal fine, $4 million is community service payments to the National Fish and Wildlife Foundation (NFWF) for the purpose of conducting research and activities in support of the arctic environment in the State of Alaska on the North Slope, and $4 million is criminal restitution to the State of Alaska. BP also served a three-year term of probation.

BP and low carbon energy

BP was among the first major oil corporations to publicly acknowledge that global warming was "real." In 1997, John Browne, Group Chief Executive, British Petroleum (BP America) stated: "To be absolutely clear - we must now focus on what can and what should be done, not because we can be certain climate change is happening, but because the possibility can't be ignored."

caption The BP corporate logo.

BP Amoco changed its name to BP in 2000, and introduced a new corporate slogan: “Beyond Petroleum.” It replaced its “Green Shield” logo with the helios symbol, a green and yellow sunflower pattern that was supposed to highlight the company’s interest in "green" fuels.

BP has supported research in "low carbon" energy and climate change at Scripps Institution, Princeton University, and the California Institute of Technology. BP is investing $500 million over 10 years to establish the Energy Biosciences Institute (EBI) hosted by the University of California at Berkeley with its associated strategic partners University of Illinois at Urbana-Champaign and Lawrence Berkeley National Laboratory. 

In its biofuels operations and planning, BP claims to apply a series of global standards and processes such as undertaking environmental impact assessments that cover issues such as water andbiodiversity. For example, BP claims it will not produce biofuels from areas of high conservation value as defined by the High Conservation Value Network.

BP was one of the first major energy companies to develop solar energy, and BP Solar is one of the largest solar manufacturers in the world with manufacturing plants in Australia (Sydney), Spain (Madrid), USA (Frederick, MD), India (Bangalore) and China (Xian).

BP began investing in wind power in 2005, and by 2010 had gross generating capacity of more than 1,200 megawatts (MW), enough to provide electricity for a city the size of Washington DC. BP has interests in operating wind farms in Fowler Ridge, Indiana, a large wind farm in the U.S. Midwest (600MW); Cedar Creek I, Colorado (300MW); and two projects in Texas (more than 200MW).


1 This section is drawn directly from a National Research Council (2003) report. 




Cleveland, C. (2013). Deepwater Horizon oil spill . Retrieved from


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