Federal official and environmental groups immediately greeted the report with scepticism, as the report spreads blame wide in what appears to be an attempt to minimize the British oil giant’s liabilities to Gulf of Mexico residents.

“This report is not BP’s mea culpa. Of their own eight key findings, the only take explicit responsibility for half of one. BP is happy to slice of the blame as long as they get the smallest piece,” said Ed Markey, a Massachusetts Democratic senator.

“BP is pushing part of the blame on to other companies that worked on the [Deepwater Horizon] rig, like Halliburton and Transocean. It is a way of disclaiming responsibility,” said Bellona President Frederic Hauge. “We believe the main responsibility lies with the operator.”

At the same time, Hauge said the report will be a critical contribution to trying to determine what, exactly, happened in the Gulf of Mexico saying, “[the report] is an important piece of the puzzle that must be added to what we know to clarify the causal relationship behind the tragic accident.

In the 193-page report released Wednesday morning on BP’s website, the British company described the explosion of the BP leased Deeppwater Horizon rig as an accident that arose from a complex and intertwined series of mechanical failures, human judgment errors, engineering design flaws, lagging operational implementation and team interfaces.

“No single factor caused the Macondo well tragedy,” BP said in a statement about the report. “Rather, a sequence of failures involving a number of different parties led to the explosion and fire which killed 11 people and caused widespread pollution in the Gulf of Mexico earlier this year.”

“You almost have to ask what actually work on this platform when you see the long line of failures that led to the accident,” said Hauge. “The gravity of the internal report undermines trust not only in BP as a single company, but the entire oil industry.”

BP’s report is far from the final word on possible causes of the explosion, as several divisions of the U.S. government, including the Justice Department, Coast Guard and Bureau of Ocean Energy Management, Regulation and Enforcement (formerly the Minerals Management Service), are also investigating.

Greenpeace immediately leapt on the conclusions drawn by the BP report, saying it was suspect because BP itself wrote the report. The environmental group also called for an immediate ban on deepwater drilling and called for the use of more clean energy.

The report is also missing crucial information about the malfunctioning blowout preventer, largely cited as the main cause of the spill, as the device was only brought to the surface on Saturday. BP did not have a chance to analyze the failed device before the company released its report. The blowout preventer was sent to a NASA facility in New Orleans where federal investigators are waiting to inspect it.

Oil company reports it began its inquiry immediately

The BP inquiry, conducted by the company’s safety chief, Mark Bly and a team of about 50 mostly BP employees, was initiated almost immediately after the April 20 explosion that killed 11 and spilled almost five million barrels – or 206 million gallons –  of oil into the Gulf of Mexico, the largest accidental oil spill ever.

Citing “a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces,” the report deflects attention away from BP and back onto its contractors, especially Transocean, which owned the rig, and Halliburton, which performed cement jobs on the well.

Investigators know the explosion was triggered by a bubble of methane gas that escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before igniting – which was reported by Bellona Web in the early days following the massive April 20 blowout.

But they don’t know exactly how or why the gas escaped. And they don’t know why the blowout preventer didn’t seal the well pipe at the sea bottom after the eruption, as it was supposed to.

The details of BP’s internal report were closely guarded, and only a short list of people saw it ahead of its release, the New York Times reported.

BP casts blame outward

The report also focuses less on decisions that BP made in designing and drilling the well than on what rig workers, mostly from Transocean, did after the blowout occurred.

“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,” BP’s outgoing chief executive Tony Hayward said in a statement.

“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.”

While BP does admit to some errors — like misreading pressure data that indicated a blowout was imminent — the report attempts to undermine the notion that the company acted in gross negligence.

Among its most significant conclusions, the report says that the blowout came up the centre of the pipe and not up the outside of the well casing — or the annulus.

If true, the finding is significant because it plays down the importance of certain BP decisions that have been criticized as negligent.

One such decision was BP’s choice of a type of well casing that internal documents indicate the company knew was cheaper but riskier. Another such decision was when BP opted to use fewer-than-advised centralizers that are meant to keep the casing properly positioned.

BP Report immediately criticised as self-serving

Because of its authorship, the report is unlikely to carry much weight in influencing the Department of Justice, which is considering criminal and civil charges related to the spill. It is, however, a first glimpse at BP’s probable legal strategy in defending itself against the charges and it represents the first in a series of such reports in the coming months.

“BP’s self penned review is a sorry attempt to spread the blame for the Deepwater Horizon oil disaster, but still reveals a devastating litany of human error, incompetence and technical failure,” wrote Greenpeace in a statement quickly on the heels of the report’s release Wednesday.

“As oil companies pursue marginal profits in challenging environments these compromises and failures are inevitable. If we want to avoid future deep water oil disasters governments need to move the world beyond oil by investing in clean energy solutions,” the statement continues, adding that “Greenpeace is calling for an immediate ban on all deep water drilling, which is the only sensible response to this disaster. The time has come to move beyond oil and invest in clean energy.”

The BP report faults Transocean workers for failing to recognize and act on the influx of hydrocarbons into the well for more than 40 minutes until the hydrocarbons were in the riser and rapidly flowing to the surface.

And the report adds that after the well-flow reached the rig it was routed to a mud-gas separator, causing gas to be vented directly onto the rig rather than being diverted overboard.

The flow of gas into the engine rooms through the ventilation system created a potential for ignition that the rig’s fire and gas system did not prevent, BP investigators found.

In recent testimony, BP executives have pointed out the blowout preventer on the rig did not go through an extensive certification as required by federal regulations, a fact which was earlier documented in internal Transocean equipment reports

“Even after explosion and fire had disabled its crew-operated controls, the rig’s blow-out preventer on the sea-bed should have activated automatically to seal the well,” the report concludes. “But it failed to operate, probably because critical components were not working.”

Inter-corporation finger pointing

In recent weeks, BP has attempted to shift blame by claiming Halliburton should be held responsible for the failures in cement work. Halliburton designed and pumped a cement seal that federal investigators have said may have allowed explosive natural gas to enter the well and rush up toward the rig.

In federal testimony, Halliburton executives have responded by arguing that they were following BP’s orders and by pointing to e-mails from April 18 in which Halliburton executives warn BP of a potential “severe gas flow problem.”

But BP executives have highlighted other internal documents provided to the New York Times that they say show Halliburton’s confidence in its cementing job.

“We have completed the job and it went well,” one Halliburton worker wrote about the cement work in an e-mail only hours before the explosion. “Full returns were observed throughout.”

However, several engineers who were asked to review the documents said that the warnings from Halliburton were clear and firm. They also pointed out that ultimate responsibility for decision-making on the rig rested with BP, the New York Times reported.