BP spreads the blame

In its report BP blamed a "complex and interlinked" series of events involving mechanical failures and human judgements for the the Gulf of Mexico oil disaster.

While accepting a portion of the blame the firm also criticised rig owner Transocean and cement contractor Halliburton.

The oil giant published the report on Wednesday afternoon, claiming it was the culmination of an independent investigation despite the fact that it was conducted by the company's head of safety and operations Mark Bly.

The investigation found shoddy cement work at the bottom of the well failed to hold gas and oil in its reservoir, which leaked into the casing.

BP and Transocean employees then incorrectly accepted negative pressure readings in the crucial minutes before the explosion and failed to spot the leak.

Further mechanical failures allowed gas to be vented directly on to the rig - where it ignited - rather than being diverted overboard.

The rig's blow-out preventer, a protective valve, should have sealed the well but failed to operate.

BP's outgoing chief executive Tony Hayward, who was forced to stand down in the wake of the disaster, said: "The investigation report provides critical new information on the causes of this terrible accident.

"It is evident that a series of complex events, rather than a single mistake or failure, led to the tragedy.

"Multiple parties, including BP, Halliburton and Transocean, were involved."

Environmental group Greenpeace called for the British government to introduce an urgent moratorium on deep-water drilling.

Greenpeace energy campaign head Jim Footner said: "This report is a sorry catalogue of the gaffes and failures behind the Deepwater Horizon disaster. And it's highly likely that a truly independent report would be even more damning for BP.

"Worryingly, they're just weeks away from drilling at similar depths in UK waters. The government must step in right now and stop this by introducing a moratorium on deep-water drilling.

"But the real problem is our addiction to oil, which is pushing companies like BP to put lives and the environment at risk."

The explosion on April 20 killed 11 workers and caused an estimated 4.9 million barrels of oil to gush into the Gulf - the largest offshore spill in history.