BP admitted today its managers on the Deepwater Horizon missed key warning signs in the hours before the explosion aboard the oil rig, but an internal investigation put much of the blame on other companies involved in the well.

A 234-page report described eight main causes for the blast, which killed 11 men and created an environmental disaster. But BP was accused of attempting to pass on the blame for its conclusion that Transocean, the rig owner, and Halliburton, which carried out cement work, shared much of the responsibility.

Mark Bly, the oil company's head of safety and the leader of the investigation, admitted that BP onsite managers could have prevented the catastrophe had they picked up warning signs of a breach of the cement seal at the bottom of the well, as well as unusual pressure test readings, only moments before the explosion.

He told reporters in Washington: "Given everything that came before, there probably should have been more risk assessment. They probably should have been more careful."

The report was widely seen as a possible preview of BP's legal strategy. The oil company was accused of trying to reduce the chances of being charged with gross negligence, which would expose it to possible criminal proceedings and billions of dollars in damage.

Within hours of its release, Transocean and Halliburton accused BP of attempting to shift attention from its own mistakes of bad well design and disregard of safety procedures. Members of Congress and environmentalists also dismissed it.

Transocean said: "This is a self-serving report that attempts to conceal the critical factor that set the stage for the Macondo incident: BP's fatally flawed well design."

Ed Markey, the Massachusetts Democrat who has been investigating the spill in Congress, said the report was more about protecting BP's interests than getting to the cause of the disaster. "BP is happy to slice up blame, as long as they get the smallest piece," he said.

Environmental organisations were more scathing. "BPs investigation doesn't pass the smell test ," said Kieran Suckling, the director of the Centre for Biological Diversity. "This report is more concerned with calming BP shareholders than taking responsibility for its actions."

There were similar sentiments in the Gulf. Alfred Sunseri, whose family-owned oyster company faces ruin after the spill, said: "When BP shows me a report of how exactly they will deal with those people most impacted by this tragedy – ie those in the fisheries-related businesses – I'll believe they are not just using their talents in public relations to dispel their liability."

Bly acknowledged the report fails to address the key charges raised in Congress and elsewhere against the oil company: that it allowed a culture of recklessness to flourish, and that it was so anxious to finish work on a project that was 43 days over time and $20m (£13m) over budget that it omitted standard industry safeguards.

The report does recognise there were gaping lapses in oversight on the Deepwater Horizon, going on to make 25 recommendations for tighter scrutiny by well owners – such as BP –of rig operations.

But Bly rejected the idea that cost-cutting had dictated BP's decisions on the rig, saying: "What we see instead is, where there were errors made they were based on poor decision-making process or using wrong information."

Oil companies could be facing tougher regulation anyway: the White House said it was asking for more funds from Congress to step up oil rig inspections.

The report is narrowly focused on the final days before the explosion rather than on earlier decisions about well design and safety procedures. It is also closely focused on the rig itself. No BP officials have been sacked for their role in the explosion, and Bly said there was no indication of any blame beyond the well-site managers.

The investigation identifies eight main causes of the explosion, putting particular blame on well integrity. It says Halliburton's choice of foam cement for the area around the well casing failed to produce a strong enough seal.

Tony Hayward, who was BP's chief executive at the time of the explosion, said in a statement: "To put it simply, there was a bad cement job."

Halliburton said it had carried out its work to BP specifications.

The report also said the blowout preventer, the last line of defence once there is a breach, had failed. There, BP pointed at Transocean noting that the battery pack on the blowout preventer had been allowed to run low.

But Bly said the disaster may have been prevented had work crews – BP's as well as Transocean's – spotted the crucial warning signs in a series of anomalous pressure test readings in the run-up to the explosion. "A fundamental to well control is early detection," he said. The pressure test readings should have alerted crews to the escape of oil and gas from the well reservoir, he said.

The report is far from the final word on the explosion and the subsequent oil spill, with Transocean, Congress and the federal government carrying out investigations.

But Robert Gordon, a lawyer for businesses affected by the spill, said it was unlikely to carry much weight in the months ahead. "BP blaming others for the Gulf oil disaster is like Bernie Madoff blaming his accountant," he said.