A US report has found "material deficiencies" in BP's safety procedures at its American oil refineries.
Led by former US Secretary of State James A Baker, the panel probed a 2005 explosion at BP's Texas City refinery, that killed 15 people and injured 180.
BP said it would implement the report's recommendations, adding it had taken significant steps to improve safety.
BBC business editor Robert Peston called the report very meticulous and extremely savage.
He went on to add that the panel's criticism against BP was very serious and went right to the top of the company.
BP's shares closed 8 pence, or 1.5%, lower at 541p in London.
The report found that prior to the Texas City tragedy, BP emphasised personal safety but not process safety, and that the problem existed at all five of the firm's US refineries.
Former US Secretary of State James A Baker led the panel
"BP mistakenly interpreted improving personal injury rates as an indication of acceptable process safety performance at its US refineries," said the report.
"The panel found instances of a lack of operating discipline, toleration of serious deviations from safe operating practices, and apparent complacency toward serious safety risks at each refinery."
Yet speaking after the publication of the report, Mr Baker said that the panel "did not find any deliberate or conscious efforts on BP's part to short-circuit safety".
BP said it had already taken steps to improve its safety performance, including forming a senior executive team to oversee all aspects of operational safety.
The oil giant also said it had increased spending on its refineries, and had earmarked $200m (£102m) to pay for safety audits and redesigns of its refinery operations.
BP added that it had also appointed retired federal judge Stanley Sporkin to deal with and investigate concerns raised by staff or contract workers.
BP's outgoing chief executive, Lord Browne, said he thanked the panel members for "their insights and their recommendations".
"We asked for a candid assessment from this diverse group of experts and they delivered one," he added.
Mr Baker's panel made 10 recommendations in total, which BP has said it will implement.
These include more effective leadership on process safety, and the transformation of the company "into an industry leader in safety performance".
BP announced on Friday last week that Lord Browne would now be standing down in July this year, 18 months earlier than initially announced.
The move came just four days before the publication of the US report.
Lord Browne is being replaced by BP's current head of exploration and production, Tony Hayward.