Oil-leak clean-up bill nears $1bn says BP

BP revealed costs so far had reached $930m (640m) – up by $170m (117m) in the past four days alone.

The group has also played down reports that its "Top Kill" operation to stop the oil leak was working, saying that success was still uncertain.

Hopes had mounted that the Top Kill plans were beginning to stem the flow of oil after a US coastguard said the well had stabilised.

The tactic of pumping mud into a leaking well has never been used at such depths before and although it appeared to have early success, it is expected to be several more days before the long term prospects will become known.

Shares in BP rose 6 per cent on the reports, but later dipped when BP announced its operation would continue for up to 48 hours more.

It is expected to be capped with concrete when the operation is

complete.

Oil has been spewing from the well since the Deepwater Horizon rig exploded and sank on April 20, killing 11 workers and sparking an environmental disaster.

BP originally estimated that oil was spilling out at about 5,000 barrels a day, but US government scientists have calculated the rate is far worse – between 12,000 and 19,000 barrels a day.

Even using the most conservative estimate, that means about 18 million gallons have spilled so far, surpassing the 1989 Exxon Valdez disaster, in which a tanker ran aground in Alaska, spilling nearly 11 million gallons.

BP is coming under increasing pressure from President Barack Obama for failing to contain the leak.

Mr Obama returned to the Gulf of Mexico coast yesterday after insisting he was taking charge of efforts to shut down the well.

He has been highly critical of BP and blamed a "scandalously close relationship" between oil firms and government regulators for a lax approach to safety in the deep oil rigs.

BP's head of communications, Andrew Gowers, has admitted the spill has been "a transforming incident" for the oil industry and the regulatory system.

As well as the Top Kill operation, BP was continuing to drill two relief wells at about 13,000ft (3,962m) below the sea bed in an attempt to cut off the flow of oil, but these are expected to take three months to complete.

It is also collecting oil from a mile-long siphon tube, but this is capturing only about 2,010 barrels a day on average and as few as 1,360 barrels on some days. Other back-up plans include the possibility of using a "cap containment system" to capture the leaking oil, which

would take some three to four days to install, according to BP.

BP is pumping cash into these efforts and to compensate those affected, including grants to the affected states of Florida, Alabama, Louisiana and Mississippi to help with their clean-up costs.

It said 26,000 claims have been filed so far and 11,650 payments have already been made.

The group has received more than 96,000 calls to its help lines.

The sums involved are already mammoth, but BP is one of the most profitable companies in the world, making $5.6 billion (3.9 billion) in just the first three months of 2010.