Shares in oil giant British Petroleum (BP) dropped sharply on the London Stock Exchange (LSE) today, following the company's admission that its "top kill" effort to seal the well had failed.
The 15 per cent plunge in the share price came as BP revealed that the total cost of its response to the April 20 incident had reached $990 million.
The company is now working on using robot submarines in the latest move to stem the flow of oil.
The remote-controlled submarines are carrying equipment and cutting small pipes some 1,524 metres below the surface of the water, in the hope of placing a containment cap over the leak.
The new attempt to stop the oil flow, which began on Sunday, should take four days to complete, the company said in a statement Tuesday.
But it also warned that the technique, known as the "lower marine riser package", or LMRP, had "never before been deployed at these depths and conditions, and their efficiency and ability to contain the oil and gas cannot be assured".
BP said it had so far received approximately 30,000 claims, half of which had already been settled, costing $40 million.
By mid-morning in London trading, BP shares were 65 pence lower at 429.7 pence, causing the Financial Times Share Index (FTSE) to dip 93.7 to 5094.7 points.
BP, one of the heavyweights of the London stock market, is a key stock for pension fund investments in Britain.