Oil is continuing to gush uncontrollably into the Gulf of Mexico, amid reports that the slick has already spread as far as Florida.
So far, efforts to cap the flow from a ruptured pipe 1,500 metres underwater have failed.
British Petroleum, which is responsible for the clean-up effort, says it has inserted a tube into the leaking pipe which is enabling it to siphon off about 40 per cent of the outflow.
The oil is then being pumped up to a ship on the surface, where a flotilla of vessels is battling to contain the slick.
“There are somewhere approximately 1,500 to 2,000 barrels a day that are being collected through the so called riser-insertion tube,” US Interior Secretary Ken Salazar told a Congressional hearing.
“The efforts are intended to ramp up over the hours ahead on a sequencing of about every two hours and we ought to have a better measure of what the flow is that is leaking out from the well.”
BP boss Tony Hayward has tried to play down the environmental impact of the spill, saying the effects would be “very modest”.
His comments come as experts warn that oil may have already been caught up in the powerful current off the Florida peninsular. Tar balls found on Key West beaches are now being tested to see if they come from the BP spill.