BP's chief executive has said the company is trying two methods to cap a leaking oil well in the Gulf of Mexico. But Tony Hayward told US television the results would not be clear for another two days.
Mr Hayward told ABC that the 'top kill' method, where heavy drilling fluid called mud is pumped into the leak to try to overcome the leaking oil, was supplemented with a so-called 'junk shot'.
That involves pumping 'loss control material... to attempt to create a bridge against which we could pump more mud,' he said. Mr Hayward warned that it was too early to tell whether either method was having any success.
Earlier, US incident commander Admiral Thad Allen said the flow of oil and gas from the broken well had been stopped by pumping mud into it, but the challenge was whether that could be sustained.
Earlier, BP admitted that the clean-up bill for the spill has soared to nearly $1 billion as scientists claim the spill is now the worst in US history. BP revealed costs so far had reached $930m (£640m) - up by $170m in the past four days alone.
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 around 5,000 barrels a day, but US government scientists have calculated the rate is far worse - between 12,000 to 19,000 barrels a day.
Even using the most conservative estimate, that means around 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.
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.
It has not been able to put a figure on the final cost, some of which it is likely to try to claim back from the owner of the oil rig, Transocean, and from insurance.
The sums involved are already mammoth, but BP is one of the most profitable companies in the world, making $5.6 billion in just the first three months of 2010.
