The report, released Wednesday, said in the days leading up to the disaster, BP made a series of decisions that complicated cementing operations, added risk, and may have contributed to the ultimate failure of the cement job.
Other companies also shared some of the blame, according to the report, which noted that Transocean, as owner of the Deepwater Horizon, was responsible for conducting safe operations and for protecting personnel onboard.
The report said BP, and in some cases its contractors, violated seven federal regulations at the time of the incident. They included the failure to take necessary precautions to keep the well under control at all times, to perform a cement job that kept the oil and gas down hole, and to maintain the blowout preventer -- which is supposed to lock in place to prevent a spill in case of an explosion -- in accordance with industry-accepted practice.
The details were contained in the final report from an investigation team of the coast guard and the agency that regulates offshore drilling. The panel held hearings in the year following the April 20, 2010, Deepwater Horizon catastrophe. The U.S. Coast Guard-Bureau of Ocean Energy Management Regulation and Enforcement investigation was among the most exhaustive.
The panel's report will be used to shape reforms to offshore drilling safety and regulation. It also will be used by lawyers for victims involved in the multibillion dollar court battle over the oil spill, and by government agencies that are considering civil and criminal charges against BP and other companies.
Other investigations spread around the blame more evenly, faulting misreadings of key data, the failure of the blowout preventer to stop the flow of oil to the sea and other shortcomings by executives, engineers and rig crew members.
The report said the decisions included using only one cement barrier and BP's choice to set the production casing in a location in the Macondo well that created additional risk of influx of oil or gas. The casing is a steel pipe placed in a well to maintain its integrity.
The panel said BP failed to communicate these decisions and the increasing risks to Transocean.
While the report recognizes that other companies had roles in the disaster, the panel said that BP was the final decision maker.
"BP, as the designated operator under BOEMRE regulations, was ultimately responsible for conducting operations at Macondo in a way that ensured the safety and protection of personnel, equipment, natural resources, and the environment," the panel concluded.
The report pins the causes for the disaster on many of the same faulty decisions found by previous probes, including those by the president's independent oil spill commission, congressional committees and the companies themselves. But it is likely to carry more weight in Congress, where Republican legislators in particular have said they are unwilling to adopt reforms until the federal investigation was complete.
Since the disaster, the Obama administration has reorganized the offshore drilling agency and boosted safety regulations. But Congress has yet to pass a single piece of legislation to address safety gaps highlighted by the disaster.
In the report's 57 findings about the disaster, only one person -- BP engineer Mark Hafle -- is mentioned by name. It said Hafle's failure to investigate or resolve anomalies detected during a critical test possibly contributed to the crew's failure to detect the initial influx of gas and oil. Hafle also chose not to run a cement log, a test that evaluates the quality of the cement job, in violation of BP procedures, the report found.
Hafle -- a key decision maker on the doomed rig -- refused to testify before the federal panel in August 2010, citing his constitutional right against self-incrimination.
The panel recommended further changes to offshore drilling practices, including requiring at least two barriers to be placed in a well -- one mechanical, and one cement. The Macondo well had a single barrier, the cement seal at the bottom, so when the blowout happened the only thing to stop it was the blowout preventer. That didn't work, the panel says, because the kink in the pipe caused by the force of the blowout kept it out of reach of the safety device's shearing rams. The rams are supposed to pinch a well shut in an emergency by slicing through the well's drill pipe.
The team also said BOEMRE should standardize testing procedures on oil and gas wells.
BP said in a statement that the British company accepts the report's conclusion that the accident was the result of multiple causes involving multiple parties. BP did not address the report's specific conclusions about the cement.
"From the outset, BP acknowledged its role in the accident and has taken concrete steps to further enhance safety and risk management throughout its global operations, including the implementation of new voluntary standards and practices in the Gulf of Mexico that exceed current regulatory requirements and strengthen the oversight of contractors," BP said. "We continue to encourage other parties to acknowledge their roles in the accident and make changes to help prevent similar accidents in the future.
Transocean and cement contractor Halliburton did not immediately respond to requests for comment.
The report paints a dark portrait of the final hours aboard the Deepwater Horizon, where the workers in the most danger were unaware of the anomalies being detected by engineers looking at data coming from the well. The federal team also charges that BP made decisions blindly, without assessing risk.
While this report and others blame BP for jeopardizing safety to cut costs, the federal panel went further and examined the 2009 performance evaluations of 13 BP employees involved on the Macondo well. All but one of the reviews cited cost savings when evaluating the employee's work. Congress has suggested BP cut corners to save money, compromising safety.
The oil spill off Louisiana spewed 757 million litres of crude from an undersea well owned by BP. The disaster caused billions of dollars in damage to hundreds of kilometres of coastline and wreaked havoc on the Gulf economy.
While the federal investigative team lays the blame for the blowout on the companies, it says the government's approval of some of the questionable decisions was not responsible for the disaster. The federal agency that oversees offshore drilling signed off on many of the calls made by the companies. Congressional leaders immediately scheduled hearings to discuss the report's findings.
House Natural Resources Committee chairman Doc Hastings, a Republican, who has pushed legislation to vastly expand offshore drilling since the disaster, said he hoped the federal government's conclusions would give legislators a clearer picture about what happened.
Rep. Ed Markey of Massachusetts, the top Democrat on the natural resources panel, called on Republicans to no longer delay efforts to reform offshore drilling. Markey has sponsored a bill to implement many of the changes suggested by the president's independent spill panel.