A United States government safety panel has said BP focused too much on personal worker safety instead of big systemic hazards that led to the Gulf of Mexico oil spill.
Eleven workers were killed in the April 2010 explosion of the Deepwater Horizon rig.
The subsequent uncontrolled discharge of crude oil lasted nearly three months and about 200m gallons of oil flowed into the Gulf from the blown-out Macondo well.
The rig was located in water more than 5,000ft deep, and the spill caused widespread environmental damage.
The US Chemical Safety Board has convened a two-day public hearing into the drilling disaster, being held in Houston, Texas.
It is expected to say in a presentation today that the oil company was not as strict on overall safety when drilling rigs involved other companies that they hired.
BP had the lease on the well, but the rig was owned and operated by another company, the Swiss-based deepwater driller Transocean.
Investigators say that contractor-owner split made a difference in major accident prevention.
Meanwhile, the Russian state oil company Rosneft said it had expressed interest in buying BP's stake in Anglo-Russian oil firm TNK-BP and will enter talks with the British firm over the deal.
"The parties agreed to commence negotiations on this matter and signed a non-disclosure agreement," Rosneft said in a statement.
The exit would end a tumultuous relationship between the pair, which was created to maximise output from Russia's vast oil reserves.
TNK-BP is Russia's third-largest oil producer and is owned on an equal basis by BP and AAR, a consortium of Russian billionaire shareholders.
Last week, AAR indicated interest in buying out BP, with a 50% stake in TNK-BP possibly worth around £11.6bn, according to the company's market valuation.
Although mired in boardroom disputes for much of its existence, TNK-BP has generated healthy returns both for the British company and the Russians.
Over the past years, TNK-BP's output has accounted for more than a quarter of BP's total global production.