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National incident commander Admiral Thad Allen gestures during one of his daily news conferences at the Department of Homeland Security in Washington, D.C. ((Cliff Owen/Associated Press))

A new estimate doubling the amount of oil that has spewed out of a blown-out well in the Gulf of Mexico is just "one portion" of a larger effort to determine the flow rate, the U.S. Coast Guard said Friday.

"We're trying to refine those numbers," Admiral Thad Allen told reporters. "One portion of the work, as we just indicated, came up with a higher flow rate."

On Thursday, a U.S. government task force, the Flow Rate Technical Group, said between 20,000 barrels and 40,000 barrels of oil might have spilled out daily before the well was partially contained with a cap on June 3.

Scientists had previously estimated about 12,000 to 19,000 barrels of oil a day had been leaking from the well since an oil rig exploded April 20. The U.S. government had put the estimate lower, at about 5,000 barrels per day.

But the head of the U.S. Geological Survey, who released the results, warned against reading them conclusively.

"Our scientific analysis is still a work in progress," Marcia McNutt said.

Boosting capture capacity

BP has been able to capture some of that oil with the containment cap. On Thursday, it captured 15,400 barrels, the company said Friday. That is 400 barrels less than it collected on Wednesday and thousands less than its capacity of 28,000 barrels, Allen said.

Allen hopes BP can eventually capture up to 50,000 barrels a day once it completes "an incremental build-out of capacity."

Production facilities and shuttle tankers that can accommodate a greater flow rate are en route to the Gulf of Mexico and are expected to be operational in mid-June or early July, he said.

"When we do that, we will shift to a containment cap which help us capture more of the wellhead," he said.