An investigation carried out by BP said it was responsible in part for the disaster, but it also blamed other companies working on the well.
BP faces billions of dollars worth of legal claims for compensation over the spill, the worst in recent US history.
An estimated 4.9m barrels of oil leaked into the Gulf after the blast.
The well was capped on 15 July, and an operation to permanently seal it is due to take place in the next few weeks.
In the 193-page internal report released on its website, BP said that decisions made by "multiple companies and work teams" contributed to the accident, which it said arose from "a complex and interlinked series of mechanical failures, human judgements, engineering design, operational implementation and team interfaces".
http://www.bbc.co.uk/news/world-us-canada-11225623