BP directors have sought to reassure investors about the company's strength, after its share price dropped by 16% on the New York Stock Exchange.
The directors said there is no justification for the fall, as the company is financially secure and has the flexibility to handle the costs of dealing with an oil leak in the Gulf of Mexico.
Shares closed down 6% in London on Thursday after earlier plunging 12%.
BP shares, which are jointly listed on the New York stock exchange, plunged nearly 16% in US trading after London closed on Wednesday, on fears that President Barack Obama would impose huge penalties on the company.
As a result, BP's UK share price opened at 345 pence on Thursday in London, down nearly 12% on the previous day's London close, and its lowest level since 1997.
The price later recovered some of the losses during London trading hours to end 6.6% lower at 365.5 pence.
In New York, BP's US shares opened up 9% versus the previous US close.
However, the recent price moves mean the company's share price has almost halved since the oil leak began on 20 April.
BP is under increasingly sharp attack by some US politicians for its handling of the spill, which described as the worst environmental disaster the United States has faced.
The leak began after an explosion and fire on 20 April on the Deepwater Horizon drilling rig, in which 11 crew members died. The rig sank two days later.
BP says the total cost is about $US1.4 billion so far, but its cash flow is strong. However, one estimate has the eventual bill at $US30 billion.
