BP said yesterday that the total cost of the oil spewing into the Gulf of Mexico had hit more than £1.1billion so far.
Almost half a million gallons of oil a day from the damaged well is now being prevented from spilling into the sea.
But the ruptured pipe is still leaking between 500,000 and a million gallons a day.
The mounting bill includes £862million on efforts to stop the flow of oil, grants to gulf states, and claims paid to those affected – as well as £249million pledged for a Louisiana project to build barrier islands to keep oil from the coastline.
The effectiveness of BP’s cap on the damaged well – installed by robot submarines a mile below the sea surface last week – is expected to improve but it is still well short of capturing all of the oil from the leak.
Analysts at Goldman Sachs cut their rating on the firm and said BP could suspend dividend payments for two quarters to help fund the rescue effort.
“The ultimate cost to BP from the Gulf of Mexico spill is impossible to know with certainty at present, given uncertainties over the total size of the spill, its impact on the local economy and longer-term impacts on BP’s competitive position in the Gulf of Mexico and beyond,” the investment bank said.
BP admitted yesterday that it would be “a few days” before the success of the project is known, while fears are mounting for the clean-up operation as the hurricane season fast approaches.
The US coastguard’s Admiral Thad Allen, who is overseeing the US government’s response to the spill, warned that the battle to contain the oil was likely to stretch into the autumn.
BP is working to increase the efficiency of the containment cap, which has been fitted to the top of broken valves on the seabed to transport captured oil and gas to a ship on the surface.
The group is putting in place an additional containment system, using the pipes from the failed “top kill” operation to block the well, which it said should be in place by mid-June.
It is also working on a way to make the cap system “more permanent” and flexible during the hurricane season.
But BP said: “This is a complex operation, involving risks and uncertainties, being carried out 5,000ft under water.”
Meanwhile, two relief wells are being drilled below the seabed to intercept the spilling well, although these will not be completed until August.
The company has also launched huge efforts to tackle the spill on the surface and protect the coast, but it has been heavily criticised in the US over its response since the Deepwater Horizon rig exploded and sank on April 20, killing 11 workers.
BP chief executive Tony Hayward and the management team have come under pressure over their positions at the helm.