Updated from 4:23 a.m. EDT
shares were trading down about 13% in London after the oil company said over the weekend the "top-kill" procedure to plug the oil leak in the Gulf of Mexico had failed.
BP shares were at 429.2 pence. The shares had plunged as much as 15% on one point during trading Tuesday.
BP said Tuesday it now plans to place a new containment valve over the blown-out well this week. BP said it wil begin cutting through the riser that's spewing oil and gas into the Gulf as soon as Wednesday, after which it will attempt to place the cap-like containment device that would siphon the mixture to the surface.
BP Photo Timeline Oil Spill Impact and Response
BP said Tuesday the cost of responding to the oil spill to date has risen to about $990 million.
"All of these operations, including the cutting of the riser, are complex, involve risks and uncertainties, and have to be carried out by (remote-operated vehicles) at 5,000 feet under water," BP said in a statement on its Web site Tuesday. "Systems such as the LMRP containment cap have never before been deployed at these depths and conditions, and their efficiency and ability to contain the oil and gas cannot be assured."
-- Reported by Joseph Woelfel in New York.
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