A new cap placed over a ruptured oil well in the Gulf of Mexico has begun to funnel oil to the surface.
US Coast Guard Adm Thad Allen said a rough estimate showed that about 1,000 barrels a day was being captured.
This is only a small part of the 12,000-19,000 a day believed to be leaking and BP says it could take 48 hours to know if the system is working.
Adm Allen stressed he could not give any certain figures on the amount being funnelled.
"Sometime later [on Friday] we'll probably be able to get an approximation of how much oil we are capturing," he said.
But he said that the amount should increase as BP shut off vents to capture more of the oil.
In a conference call to investors, BP chief executive Tony Hayward said it could take 48 hours before the system was optimised and a determination made on whether it had succeeded.
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