On April 20, 2010, the Deepwater Horizon, a mobile offshore drilling unit leased by BP, was finishing work on the Macondo well some 41 miles off the Louisiana coast when gas from the well shot up the riser and exploded across the rig. Eleven crew members were killed. The rig burned for a day and a half and sank on April 22.
With the rig gone, oil poured from the wellhead on the seafloor, nearly a mile beneath the surface, for 87 days. Containment domes, a "top kill" and other attempts failed until the well was capped on July 15, 2010, and finally killed that September. It was the largest marine oil spill in United States history; a federal court later determined that 3.19 million barrels of oil were discharged into the Gulf of Mexico.
The joint investigation by the Bureau of Ocean Energy Management, Regulation and Enforcement and the U.S. Coast Guard (2011) found that the blowout resulted from failures in the cement job and other barriers meant to seal the well, that BP and its contractors misread a negative pressure test which showed the well was not secure, and that the blowout preventer’s emergency systems failed to shear the drill pipe and seal the well. The National Commission appointed by the President reached a broader conclusion: the disaster grew out of systemic failures by the drilling industry and by the regulators charged with overseeing it.
The aftermath included a six-month moratorium on deepwater drilling, the breakup of the federal offshore regulator into separate agencies, and tougher rules for well control and blowout preventers. BP’s costs passed $65 billion, including a $20.8 billion settlement with the United States and the five Gulf states — the largest environmental settlement in American history.
Download the Joint Investigation Report — Volume II: Causes of the Blowout (1.9 MB file)
Download the National Commission Report to the President (17.7 MB file)