A report by BP (BP) says that "multiple companies and work teams" are responsible for the Gulf oil disaster that killed 11 workers and spewed out millions of gallons of oil into the ocean.
"It is evident that a series of complex events, rather than a single mistake or failure, led to the tragedy," outgoing CEO Tony Hayward said in a statement. "Multiple parties, including BP, Halliburton and Transocean, were involved."
The report by BP blames the accident on a range of factors, including the cement used at the bottom of the Macondo well, misreading of the results of a pressure test by BP and Transocean staff, and the failure of the rig's blow-out preventer to activate.
The report is the conclusion of a four-month investigation carried out by Mark Bly, BP's safety and operations chief.
"Based on the report, it would appear unlikely that the well design contributed to the incident, as the investigation found that the hydrocarbons flowed up the production casing through the bottom of the well," Hayward said.