Who was responsible for the Gulf of Mexico oil leak in 2010: BP, Transocean, or Halliburton?

Catastrophic damage to an offshore oil well in 2010 caused an explosion on the Deepwater Horizon oil rig that killed eleven workers and leaked an estimated nearly 5 million barrels (206 million gallons) of oil into the Gulf of Mexico. The oil leaked continuously from the well, which was located a mile beneath the ocean's surface, beginning after the explosion on April 20 and lasting until the well was finally plugged in August and declared permanently sealed in September. Pinning responsibility on a single entity proved difficult as the several companies involved pointed fingers at each other.

BP owned the well but blamed the accident on Transocean, the owner of the failed blowout preventer device. BP's initial message to the public was that they did not cause the accident but they would take responsibility for the cleanup. The executive editor of Advertising Age was quoted in the New York Times as calling this "a fine line between what they want to say for legal reasons and what consumers want to hear".

BP's CEO Tony Hayward told the BBC on May 6, 2010 that his company "will be judged not on the basis of an accident that, you know, frankly was not our accident."

At a May 11 hearing before the U.S. Senate Energy and Natural Resources Committee, representatives of three oil companies blamed each other for the accident. Halliburton, which cemented BP's well, claimed to have met BP's stated requirements for the task and cited the failure of Transocean's blowout preventer. Transocean's CEO said the blowout preventer was successfully tested a week before the accident; he also blamed BP and Halliburton for the inadequate cementing believed to have led to the explosion. BP's president said that Transocean, as owner/operator of the drilling rig, was responsible for safety.

President Obama later complained, "I did not appreciate what I considered to be a ridiculous spectacle during the congressional hearings into this matter. You had executives of BP and Transocean and Halliburton falling over each other to point the finger of blame at somebody else. ...it is pretty clear that the system failed, and it failed badly."

In an interview on CBS's "60 Minutes" on May 16, explosion survivor Mike Williams described how problems on the Deepwater Horizon had been ignored in the past. Rep. Ed Markey (D-MA) told reporters, "BP has lost all credibility," and, furthermore, he warned of the extent of the ongoing leak, "it is clear that they have been hiding the actual consequences of this spill."

On June 8, federal authorities asking BP to immediately provide containment plans for the leak and contingency cleanup plans for the upcoming hurricane season. BP said that a new, better-fitting cap on the leaking well would be implemented in early July. The next day, as reported by CNN, BP submitted "a three-element plan that included the current container cap, a choke line to pump additional oil to the surface and a kill line intended to capture oil left in excess after the first two methods. The kill line...would not be operational until mid-July, a date that was unacceptable to the government."

Later that month, the CEO of Anadarko Petroleum Corp., which owned a 25 percent stake in the well, accused BP of "gross negligence or willful misconduct". BP's CEO Tony Hayward denied this and said he expected Anadarko to "live up to their obligations." Anadarko eventually agreed in October 2011 to pay $4 billion to BP as part of a settlement.

Government bureaucratic incompetence was also blamed. Only weeks after the leak began, Secretary of the Interior Ken Salazar said that the Minerals Management Service would be restructured. The same government agency had been responsible both for collecting money from oil companies and for enforcing their environmental compliance. In the future, these tasks would be managed by separate agencies.

At a House subcommittee hearing on June 15, 2010, Rep. Markey complained that the five largest oil firms – ExxonMobil, Chevron, ConocoPhillips, BP, and Shell Oil – had written disaster response plans using "the exact same words" and obviously had spent "zero time and money" on them. Rep. Henry Waxman (D-CA) pointed out that four of these firms explained how they would protect walruses in the Gulf of Mexico, when there are none for thousands of miles.

On June 17, when questioned by Congress about why BP designed a riskier well that saved the company $7-10 million, BP CEO Tony Hayward said that it wasn't his personal decision, adding: "I am not a cement engineer," "I am not a drilling engineer," and "I'm not an oceanographic scientist" when asked about those specific areas. Hayward said that the majority of the company’s safety violations over the five previous years – 760 violations at BP, compared to 8 at Sunoco, 8 at ConocoPhillips, and 1 at ExxonMobil – occurred in 2005 and 2006 before he became CEO. That same day, The Economist reported: "After adjusting for declines in the wider stockmarket, about $90 billion has been wiped off the combined value of BP (which has a 65% stake in the stricken field), its two minority partners, Anadarko and Mitsui, and the rig’s owner, Transocean. About $65 billion of this relates to BP alone."

Slowly, BP's share of the responsibility came to light. For example, BP decided to run only one pipe down the length of the well. This increased the risk that a gas bubble would rush up the pipe, so contractors recommended 21 centralizers when cementing the pipe, but BP used only six. A BP manager sent an email on April 16 regarding this decision: "Who cares, it's done, end of story, will probably be fine."

A Congressional investigator provided a document to the New York Times showing that BP chose the riskier of two methods when sealing the well. In the absence of an industry standard, they chose a single-barrier casing that would make it easier for them to drill into the same hole in the future rather than a double-barrier option to protect against gas leaks.

The chief mechanic for the Deepwater Horizon testified on June 1 at the Congressional hearing that, on the morning of the explosion, Transocean crew members had argued with BP's well site leader who insisted on using saltwater instead of heavier drilling fluid. "Well, this is how it's going to be," the BP leader told the crew, according to the witness. BP officials said in Washington that the crew did not pump in enough liquid to buffer between water and drilling mud. The pipe gave a reading of zero on the "negative pressure" test, not because the well was properly sealed, but because it was clogged with the fluid.

Additionally, workers from the drilling services contractor Schlumberger left without performing a "cement bond log" test. Later in the day, rig workers knew that gas was escaping through the cement. The explosion occurred that evening.

As the lead operator of the offshore drilling project, BP is responsible under the federal Oil Pollution Act of 1990 for all cleanup costs up to $75 million, and possibly more if found at fault. A proposed "Big Oil Bailout Prevention Act" (S. 3305) would have raised the liability cap to $10 billion and would have been made retroactive to apply to the 2010 leak, but it never became law. In any case, BP voluntarily paid significantly more than its legal obligations.

In June 2010, BP agreed to fund a $20 billion fund for victims' compensation. A year and a half after the explosion, BP's website indicated that over $7 billion had already been paid out of escrow. The company's efforts included skimming or burning over one million barrels of oily liquid from the ocean's surface, making payments to unemployed oil rig workers, granting money to affected U.S. states, and founding the Gulf of Mexico Research Initiative. Due to these expenses, the company reported a $4.9 billion loss in 2010.

By contrast, Transocean's CEO received a raise and the company called 2010 its "best year" in safety despite the deaths of its employees in the Deepwater Horizon explosion, although it was later compelled to apologize.

In January 2011, a U.S. government commission on the oil leak delivered its 380-page final report to the President. They reiterated the conclusion of the Columbia space shuttle investigation: "complex systems almost always fail in complex ways."

Following its own internal investigation in 2010, BP continued to place some blame on Halliburton and Transocean; those companies continued to blame BP's well design.

The costs of the accident will haunt BP for years to come. At the time the leaking well was permanently sealed on Sept. 19, 2010, BP said that the spill had already cost it $9.5 billion and would eventually cost it $32 billion. Since then, the payouts and projected costs have continued to increase. In July 2013, PBS NewsHour reported that "BP says it has spent $25 billion so far. That includes money for claims the company has paid out in the form of a multi-billion-dollar settlement that keeps growing and the cost of cleanup and remediation. It doesn’t include another $4.5 billion in fines it owes the government over the next five years. BP has set aside as much as $42 billion for a total potential tab when all is said and done." Image above: Fire boat response crews battle the Deepwater Horizon fire in the Gulf of Mexico. Photo by the U.S. Coast Guard. © public domain, Wikimedia Commons.


Originally posted to Helium Network on Nov. 28, 2011.

Bill McKibben says (July 6, 2024): "Truly mindblowing irony alert: the huge new LNG terminals being built in the Gulf—the biggest global warming machines on earth—come with 26 foot tall seawalls to keep out the rising seas."

Timeline of the BP/Transocean/Halliburton oil spill in the Gulf of Mexico in 2010

An explosion in an undersea oil well caused an environmental catastrophe when hundreds of millions of gallons of oil leaked into the Gulf of Mexico in 2010. Below is a timeline of the first two months of the incident.

April 20-26: The well explosion, the sinking of the Deepwater Horizon, and the attempt to activate the blowout preventer

The oil company BP had been drilling an exploratory well in the Macondo oil deposit a mile under the surface of the Gulf of Mexico. The Macondo 252 well was drilled to a depth of a little over 18,000 feet (including the depth of the sea water) about 40 miles offshore from southeast Louisiana.

BP owned the well, and contracted Transocean Ltd. to drill it and Halliburton Energy Services Inc. to cement it. Transocean owned and operated the drilling rig named "Deepwater Horizon" which BP was leasing for a half-million dollars per day in a three-year contract. Transocean also owned and operated an emergency shut-off valve on the well known as a "blowout preventer" that was manufactured by Cameron.

Methane gas exploded from the well around 10 p.m. on April 20, for reasons likely due to the failure of the well's cement casing that had been completed by Halliburton the previous day. The monitoring systems had indicated problems with the pressure in the well around 9 p.m. and the pump had been shut down 18 minutes before the explosion. Propelled from a depth of 5,000 feet, traveling up toward the rig through a riser pipe, the gas caused the Deepwater Horizon to catch fire amidst a shower of a clay-water mixture used in drilling that is known as "drilling mud". For several minutes, water and mud shut from the 242-foot derrick. It stopped briefly, but then noxious black smoke shot from "a goosenecked pipe on the starboard side of the deck." This was followed by an explosion and a fireball. The derrick spat fire and mud. Workers, many severely injured, began to get into lifeboats.

At the time of the explosion, BP executives were in living quarters under the work deck. They had been on board to celebrate the Deepwater Horizon's seven years without a workplace safety accident resulting in lost time. Following Halliburton's completion of the cementing, rig workers had begun to set a second seal on the well head, and the well was anticipated soon to go into production.

Out of 126 workers on the rig, 15 were injured and 11 missing men were presumed dead: Transocean employees Jason Anderson, Aaron Dale Burkeen, Donald Clark, Stephen Curtis, Roy Wyatt Kemp, Karl Kleppinger, Dewey Revette, Shane Roshto and Adam Weise; and drilling mud supplier M-I SWACO employees Gordon Jones and Blair Manuel.

Anderson's father said the Transocean employees had been on the "drilling floor" of the rig, trying to control the pressure surging from the underwater well, when the riser exploded a few feet away from them. Elton Johnson, a witness to the accident, said that when Burkeen felt the first small explosion, he tried to lower his crane as best as possible and was running for safety when the much larger explosion hit.

The surviving 115 workers, mostly Transocean employees, were evacuated to a nearby rig. According to attorneys Steven Gordon and Kurt Arnold who represent some of them, they were held on the water for 15 hours as they watched the Deepwater Horizon burn, then escorted into a hotel in the middle of the night, where, prior to being allowed to phone their families and their lawyers, Transocean asked them to initial a statement denying having witnessed the accident or having sustained any injuries.

Despite attempts to put out the fire, the half-billion-dollar Deepwater Horizon sank two days later. The mile-long pipe known as a "riser," which had an internal diameter of 19.5 inches and had connected the Deepwater Horizon to the undersea oil well, bent and fell to the ocean floor.

According to BP and the U.S. government, the riser was not discovered to be leaking oil until April 24. For unknown reasons, the 48-foot-tall, 450-ton blowout preventer had not activated properly and had only partially sealed the well.

On April 26, remote-controlled submersible robots tried, but failed, to activate the blowout preventer valve to completely seal off the well. As BP estimated that oil was leaking at about 1,000 barrels per day (a barrel is 42 gallons), the visible oil spill stretched 80 miles across the ocean's surface. Over the next few days, it widened and moved closer to Louisiana's shore.

April 28 - Estimate increased to 5,000 barrels per day

On April 28, the U.S. government raised its official estimate of the leak to 5,000 barrels of oil per day. The next day, Homeland Security secretary Janet Napolitano declared the spill to be "of national significance," clearing the way for various types of federal assistance.

May 2 - BP begins drilling the first relief well

Using a drilling rig owned and operated by Transocean, BP began drilling a second well to intersect the first, a strategy recognized as the only permanent solution to the leak. The relief well would be a half-mile from the leaking well and was intended to intercept the leaking well at its base 13,000 feet below the seabed. After its completion, drilling mud would be injected through the relief well and into the leaking well. Eventually, the oil would no longer be able to push up past the weight of the drilling mud. The relief well was estimated to take three months to complete. A second relief well was planned as an additional precaution.

May 5 - BP plugs one of three leaks in the pipe

BP plugged the smallest of three ruptures in the riser, but this did not reduce the amount of oil spilling into the ocean. Eighty-five percent of the leaking light-sweet crude was now coming from the end that had broken off the Deepwater Horizon and lay on the sea floor, while the remainder was coming from a ruptured kink lower in the pipe.

May 6 - Oil makes landfall

On May 6, the first toxic, pink, oily seawater reached the shore of Freemason Island on the Chandeleur barrier island chain off Louisiana. In the weeks to come, thick oil would coat the shores. Hundreds of dead and dying sea turtles and birds would be recovered by wildlife officials.

By May 19, scientists and government officials and agencies around the world, including the European Space Agency, agreed that at least some oil had entered the "loop current" that circulates between the Yucatan Channel, the Florida Keys, and the Bahamas.

May 7-12 - The "top hat" method of containing the leak

On May 7, BP workers guided robots to place a four-story-high, 100-ton concrete and steel containment dome over the larger of the two leaks, with the intention of siphoning oil from the dome via a mile-long steel pipe into a tanker on the surface. This containment method had never before been attempted at such a depth. Warm water and methanol were used as antifreeze to prevent the pipe from being clogged by hydrates that form in cold temperatures and high pressure; unfortunately, hydrates filled the dome itself and the project had to be discontinued.

After the failure of the large dome to siphon oil from the major leak, BP lowered a five-foot-high dome on May 12 in case it was needed in an attempt to cover the smaller leak. The dome was kept on the sea floor but was never positioned over the leak.

May 14 - Siphoning oil through a tube

On May 14, BP engineers began using robotic submarines to insert a 4-inch tube into the ruptured riser pipe that would siphon some oil a mile upward to the surface. After two days of setbacks, the tube began to siphon oil to the surface. The volume of oil traveling through the tube was increased slowly to avoid the hydrate formation that had doomed the large containment dome.

On May 17, BP's COO Doug Suttles told NBC's "Today" show that the tube was siphoning over 1,000 barrels per day; BP reported on May 20 that this amount had increased to 5,000 barrels per day. Given that the tube was only siphoning a fraction of the spill, the leak was instantly recognized to be much larger than the previous estimate of 5,000 barrels per day.

May 26-29 - "Top Kill" and "Junk Shot"

Three attempts at a "top kill" method involved a total of 30,000 barrels of drilling mud injected into the well by a 30,000-horsepower pump at rates of up to 80 barrels per minute. Sixteen attempts at a "junk shot" involved injecting debris such as shredded plastic, knotted rope, and golf balls-referred to as "bridging materials"-into the blowout preventer.

Carried out despite the risks of further puncturing the pipes or dislodging debris that was usefully blocking the pipes, these methods unfortunately failed to stop the leak.

May 22-27 - Assessing government involvement; Estimate increased to 12,000-19,000 barrels per day

On May 22, Pres. Obama ordered the creation of a bipartisan National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling to investigate the causes of the spill and recommend precautions for the future.

In response to a challenge at a press conference on May 24 about whether BP could "get out of the way" and the government could "step in" more, National Incident Commander and Coast Guard Admiral Thad Allen pointed out that "to work down there you need remotely operated vehicles; you need to do very technical work at 5,000 feet. You need equipment and expertise that's not generally within the...federal government in terms of competency, capability or capacity."

On May 27, scientists from the U.S. Geological Survey released estimates of the leak at 12,000 to 19,000 barrels per day and declared the spill to be the largest in U.S. history, surpassing the Exxon Valdez tanker spill in Alaska in 1989. Pres. Obama ordered the suspension, until a safety review could be completed, of planned lease sales in the Gulf and off Virginia and of planned exploratory wells in the Gulf and the Arctic.

May 29 - June 3 - Cutting the riser pipe

On May 29, Rear Admiral Mary Landry directed BP to begin the new tactic of cutting the leaking riser pipe and placing a containment dome over it. BP workers immediately began to build a cap to fit the lower marine riser package (LMRP). Warm water was circulated to prevent freezing. Initially, BP said the volume of oil was not expected to increase significantly when the riser was cut.

On June 2, a diamond-edged saw was stuck in the riser for several hours. It was removed, found to be jammed, and retired, ending hopes of getting a clean cut to allow a tight seal for the LMRP. BP returned to using the giant robotic arm that successfully made the first cut in the riser the previous day. This rougher cut would accommodate a fresh attempt at the "top hat" method that had been unsuccessfully attempted on May 7. The pipe was successfully cut and capped on June 3. The cutting was subsequently believed to have increased the flow, but it was unclear by how much.

June 4-20 - Siphoning from the riser; Estimate increased to 35,000-60,000 barrels per day

After beginning siphoning from the LMRP on June 4, BP retrieved about a third of the high end of the government estimate of 19,000 gallons leaking daily. Some oil was still escaping, by design, through vents in the top of the containment dome so that cold water would not enter and form hydrates. BP planned to close the vents slowly. The maximum that could be funnelled through the containment cap was 15,000 barrels per day, a milestone reached on June 7. The next day, on NBC's "Today" Show, BP COO Doug Suttles anticipated that the implementation of an auxiliary system to siphon up to an additional 10,000 barrels per day would "capture the vast majority of this flow" and that the spill "should be down to a relative trickle" by June 14 or 15.

Instead, on June 15, the government estimate of the leak was increased to 35,000 to 60,000 barrels per day, and siphoning was suspended due to a fire aboard the drilling ship Discover Enterprise, which BP attributed to a lightning strike. Even when the second containment system began siphoning oil from the blowout preventer to another ship called the Q4000 on June 16, the total capacity of both systems was only 28,000 barrels per day.

Oil recovery was stopped again on the Discovery Enterprise again on June 18 for ten hours because a safety vent called a "flame arrester" was blocked.

Hopes were still pinned on the relief wells to provide a permanent stop to the leak.

Updates

The article above was posted to Helium Network on June 20, 2010 while the well was still leaking. Updates are provided below.

August

During the first week of August, a procedure called a "static kill" failed to stop the leak.

NOAA stated on Aug. 18 that 22 percent of Gulf waters remained closed to fishing.

A report in the journal Science on Aug. 19 said that the chemical ingredients of oil had been detected three miles from the leaking well and traveling southwest in the water. This was the predictable result of having used 1.8 million gallons of chemical dispersants to drive the oil away from the surface. An underwater mass spectrometer proved that it was the same oil that was leaking from the Macondo well. An article in the Washington Post called it "a 22-mile-long invisible mist of oil" that was floating between one-half mile and one mile beneath the surface. Small fish and crustaceans live there and could potentially bring the oil up the food chain.

On Aug. 21, the research vessel Oceanus departed to find where the oil was going. Scientists aboard the ship reported a few weeks later that much of the oil seemed to have settled to the sea floor, as they found "a substantial layer of oily sediment stretching for dozens of miles in all directions." Scientists described the oil as "fluffy" and "porous" and "more than 2 inches thick" and "all over the place" and containing "recently dead shrimp, worms and other invertebrates."

Sept. 8

BP released a report of its internal investigation into the accident on April 20. It found many causes, including BP employees accepting a negative pressure reading that turned out to be wrong, problems with the cement provided by Halliburton, and a failed blowout preventer provided by Transocean.

Sept. 19

The U.S. Department of the Interior's Bureau of Ocean Energy Management declared that the well was finally sealed. This was achieved with a "bottom kill" method that involved BP drilling a separate well that connected to the leaking well and poured concrete into it. The U.S. government believed that the accident had leaked 4.9 million barrels (206 million gallons) of oil into the ocean.

CNN recapped the previously unsuccessful methods: “The rig's blowout preventer, a massive fail-safe device at the seabed, failed to operate after the blast. Efforts to activate it using remote submarines failed. An effort to plug it with heavy drilling fluid and cement failed. A bid to jam it shut by pumping it full of debris also failed.”

January 2011

The National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling produced its final "Report to the President. The report was titled "Deep Water: The Gulf Oil Disaster and the Future of Offshore Drilling."

2014

Halliburton settled for $1.1 billion.

April 2020

"The question of whether we’re any better off — my concern is we’re actually headed towards the exact same type of circumstances that were in place [then]."
- Elizabeth Johnson Klein, the Interior Department associate deputy secretary during the Obama administration, April 2020

Image credit

Image above: Public domain. Taken by Petty Officer 2nd Class Justin Stumberg. U.S. Navy Photo ID 100506-N-6070S-371. Wikimedia Commons.

The Walrus and the Oil Man: A parody of 'The Walrus and the Carpenter'

A poem about the 2010 oil spill in the Gulf of Mexico. Based on "The Walrus and the Carpenter" by Lewis Carroll in "Through the Looking-Glass".

The rig was drilling in the sea,
      Drilling with all her might –
She did her very best to pump
      The mud that makes it right –
Yet still there was a pressure change
      Near ten o’clock at night.

The sea had salty purity,
      The sparkling sands were dry.
You could not see a cloud, because
     The sun had quit the sky –
The pelicans flew off to bed,
      Politely passing by.

The Walrus and the Oil Man
      Colluded in First Class
When suddenly up rocketed
      A fireball of gas – 
Farewell the boat, farewell the crew,
      As for the sea – alas!

“If forty thousand janitors
      Each brought a paper cup,
Do you suppose,” the Walrus said,
      “That they could mop it up?”
“I doubt it,” said the Oil Man,
      So smartly clamming up.

The Walrus and the Oil Man
      Sailed on a month or two;
The oysters smiled and waved at them
      And shouted, “God bless you!”
And this was odd, considering
      The creeping toxic brew.

“The time has come,” the Walrus said,
      “To fault-find on these grounds:
On oysters – ships – and blown cement –
      On permitting – and pounds –
On accidents of Christmas Past –
      And how a dead whale sounds.”

“I weep for you,” the Man replied,
      “I deeply sympathize.
Big Oil loves all living things
      From large to smallest size!”
He turned to face the cameras
      With lightly streaming eyes.

“I drafted,” said the Oil Man,
      “A plan to guard the health
Of every walrus in this sea.”
      None grinned with tusky mouth –
And this was scarcely odd, because
      They don’t live in the South.

Poem by Tucker Lieberman, June 2010. Based on “The Walrus and the Carpenter” by Lewis Carroll in his book “Through the Looking-Glass,” 1872.)

Photos:

A young loggerhead sea turtle (Caretta caretta) photographed near Panama City, Florida in 2011. Photo by NOAA. © public domain (taken by a U.S. government employee). Wikimedia Commons.

A walrus on the ice in Alaska's Bering Sea. (They don't live in the South.) Photo taken by Captain Budd Christman, NOAA Corps © public domain (taken by a U.S. government employee). Wikimedia Commons.

Poem originally posted to Helium Network on June 23, 2010.

US: Deepwater Horizon leaked 4.9 million barrels of oil into Gulf of Mexico

The BP/Transocean oil rig "Deepwater Horizon" caused a leak on the sea floor while drilling for oil in 2010. Oil gushed into the Gulf of Mexico for months.

Image: Fire boat response crews battle the Deepwater Horizon fire in the Gulf of Mexico. Photo by the U.S. Coast Guard. © public domain, Wikimedia Commons.

Article originally posted to Helium Network on March 10, 2011.

On April 20, 2010, a rig called the Deepwater Horizon suffered an explosion while drilling for oil off the coast of Louisiana. Oil began leaking from the ocean floor, a mile beneath the water's surface, deeper than any human worker could travel to examine or fix it, and the flow was not completely stopped for nearly three months. At the end of 2010, the U.S. government's final estimate of the total spill size was 4.9 million barrels (over 200 million gallons), or an average of roughly 60,000 barrels per day over the course of the leak.

The size of the spill is relevant both in terms of its environmental impact and in the amount of fines the responsible company BP would owe to the U.S. government. Under the Clean Water Act, BP could be fined $1,100 per barrel and up to $4,300 per barrel if the company is found negligent, entailing tens of billions of dollars in fines, far outstripping the worth of the lost oil itself. (BP also paid over $10 billion to halt and clean up the spill and created a $20 billion fund called the Gulf Coast Claims Facility to settle hundreds of thousands of claims from affected individuals and small businesses.) In early 2011, BP was arguing the government should significantly reduce its estimate of the spill size.

Early estimates

In the short term, immediately after the explosion, estimates of the spill size also affected rational decisions about how to organize the cleanup response, as well as more visceral responses such as panic among the local population, public perception of BP, and satisfaction with the local, state, and federal government responses. Therefore, the U.S. government immediately began speculating about the magnitude of a possible leak, although the leak had not yet been confirmed to exist. Rates were typically reported in "barrels per day" or "b/d," where a barrel is 42 gallons (just shy of 159 liters).

The day after the explosion, the Coast Guard warned of a leak of 8,000 b/d in the event of a complete blowout at the site of the leak. On April 23, the Coast Guard logs had revised that estimate upward to 64,000-110,000 b/d, as reported by the New York Times on June 3.

The actual leak was detected four days after the explosion. Oil was leaking from the base of a mile-high "riser" pipe that connected the well on the ocean floor to the rig on the ocean surface. Although the leak could be seen on camera, its size remained difficult to calculate.

A confidential document from the U.S. National Oceanic and Atmospheric Administration (NOAA) dated April 28 expressed fear that deterioration of the riser pipe due to sand particles forced through at high pressure could cause the recently discovered leak to grow by an order of magnitude. That is, assuming a leak of 5,000 b/d, the leak could grow to 50,000 b/d.

Increasing estimates

On May 1, SkyTruth published an analysis by Florida State University oceanographer Ian R. MacDonald who placed the flow rate at a minimum of 26,500 b/d based on aerial imaging of the oil that had risen to the surface. The estimate was a minimum because he did not try to account for oil that evaporated, sank or mixed with water or that was recovered by workers.

After a closed-door meeting on May 4 with the three oil companies involved in the accident, Rep. Edward Markey (D-MA), chair of the House Energy and Environment Subcommittee, warned the press that the leak could increase to 60,000 b/d. "It's pretty clear that there was not proper preparation for the worst-case scenario," he said. The New York Times reported federal officials acknowledged that an unchecked flow could be over 100,000 b/d. Ira Leifer, a marine scientist serving on the government's Flow Rate Technical Group to estimate the spill size, said on June 7 he'd seen "nothing inconsistent with BP's worst case scenario" of 100,000 b/d. This impressively large, round number was "rediscovered" by the press on June 20. BP responded by saying the flow was unlikely to reach that point as long as the 450-ton blowout preventer remained atop the well. Although the blowout preventer had failed in its purpose of preventing a leak, by its sheer size it was partially plugging the leak, and BP said they had no plans to remove it until the flow was completely stopped.

On May 13, Steve Werely, a researcher at Purdue University, analyzed the visible particles in video of the underwater leak and told the press he believed the well was leaking 70,000 barrels per day. BP immediately publicly disputed this amount, pointing out that three-quarters of the apparent volume was methane gas. On June 9, Wereley, by then on the flow rate study team assembled by the Coast Guard and headed by the U.S. Geological Survey director, told the AP that 19,000 to 43,000 b/d would be a "reasonable conclusion." On May 27, scientists from the U.S. Geological Survey released estimates of the leak at 12,000-19,000 b/d, and possibly as high as 25,000 b/d, concurring with BP that what was leaking was mostly methane gas by volume.

With the release of ten-day-old data suggesting the total spill was between a quarter-million and a half-million barrels and still climbing, government scientists declared the spill to be the largest in U.S. history. The Exxon Valdez, the largest spill until that point, had leaked a quarter-million barrels into Alaska's Prince William Sound in 1989.

Difficulties in estimating

One difficulty in measuring the spill size was that much of the oil remains underwater. On May 16, Samantha Joye, a professor at the University of Georgia, said the underwater plumes of oil are too many to count. One was measured at 10 miles long and 3 miles wide. On June 4, researchers at the University of South Florida also confirmed the existence of plumes, of unknown lengths and up to 6 miles wide. BP Managing Director Bob Dudley argued:

"The science of the plumes hanging in the water doesn't feel right. What happens is dispersant [i.e., chemicals deliberately applied to disperse the oil] breaks the drops down into small drops, and they move around and break down."

Using robots on the ocean floor, BP cut through the twisted riser pipe to be able to fit a cap snugly over it, knowing that this could increase the flow of oil from the pipe but hoping to be able to capture most of that oil with the cap. After the pipe was cut, everyone agreed that the flow had increased - but by how much? Only by 4 to 5 percent, according to Marcia McNutt, director of the U.S. Geological Survey and chair of the National Incident Command's Flow Rate Technical Group. This increase was on top of a volume estimated, after BP's release of high-definition video upon Congressional demand, to have been 20,000-40,000 b/d. Or perhaps by 20 percent, according to Coast Guard Adm. Thad Allen on June 8. Or by "multiple factors" according to Ira Leifer.

Resolution of the oil leak

On June 10, BP said that its cap on the well was successfully capturing and funneling about 16,000 b/d. The total leak, then, had to have been at least that size. On June 15, the Deepwater Horizon Incident Joint Information Center - including Marcia McNutt, Secretary of Energy Steven Chu, and Secretary of the Interior Ken Salazar - issued a revised estimate of the leak between 35,000-60,000 b/d.

In mid-June, BP used remote-controlled submarines to deploy pressure sensors on the well to measure the flow, and the expanded containment system began capturing and burning oil at its peak capacity of over 1 million gallons per day (about 24,000 b/d). The government estimate of the leak was increased to 1.5 million to 2.5 million gallons per day, meaning that significantly more oil was leaking than BP was managing to capture and burn. Final government estimates resembled the higher end of this estimate. The leak was declared completely plugged on July 15.

There are various scientific methods for estimating the rate of an oil leak, all of which carry uncertainties. No one will ever know exactly how much oil was released into the ocean. It is important, however, to settle upon a rough number. This number is useful for scientists and others who work in ecological restoration; those who work in natural resource industries such as fishing; and for judges, lawyers and politicians determining BP's legal responsibilities.

Update: Fourteen years after the Gulf of Mexico oil spill, endemic fishes face an uncertain future, phys.org, April 18, 2024