BP reports that a sequence of failures from a number of different participants resulted in the tragic Macondo blowout that killed 11 people in the US Gulf of Mexico earlier this year. In addition to human error, the report cites "a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces."

The report is compiled from four months of intensive investigation by BP's Head of Safety and Operations, Mark Bly. In addition, the investigation was carried out independently by a team of 50 technical specialists drawn from within BP and other portions of the industry.

The report states that cement and shoe track barriers failed to contain hydrocarbons within the reservoir (per design) allowing gas and liquids to flow up the production casing; it also states that the negative pressure test was incorrectly accepted by both BP and Transocean, even though well integrity had not been determined; the Transocean rig crew is deemed to have overlooked the inflow of hydrocarbons in the well for a period of more than 40 minutes, by which time the hydrocarbons had entered the riser and were flowing to surface; the well-flow was routed to a separator at the rig surface causing gas to be vented directly to the rig floor rather than diverted overboard; the flow of gas into the engine rooms caused the gas to ignite; finally, even after the resulting explosion disabled the crew-operated controls, the rig's BOP failed to operate due to the malfunction of critical components. BP's outgoing executive, Tony Hayward stated, "To put it simply, there was a bad cement job and a failure of the shoe track barrier at the bottom of the well, which let hydrocarbons from the reservoir into the production casing. The negative pressure test was accepted when it should not have been, there were failures in well control procedures and in the blow-out preventer; and the rig's fire and gas system did not prevent ignition." Contrary to earlier assumptions, the reports denies that well design was an unlikely factor in the blowout. To view an expanded version of this report and accompanying comments visit: http://www.bp.com/genericarticle.do?categoryId=2012968&contentId=7064893