Oil floats in the Gulf of Mexico near Grand Isle, Louisiana. As much as 40,000-plus barrels of oil per day are pouring from BP's ruptured well in the Gulf of Mexico, a US official said Thursday, more than doubling the previous government estimate.

As much as 40,000-plus barrels of oil per day are pouring from BP's ruptured well in the Gulf of Mexico, a US official said Thursday, more than doubling the previous government estimate.

"The lowest estimate that we're seeing that the scientists think is credible is probably about 20,000 barrels, and the highest that we're seeing is probably a little over 40,000," Marcia NcNutt, director of the US Geological Survey and chair of a US-government-led flow rate assessment team, told reporters.

The figures -- which estimate the flow rate prior to BP cutting a busted riser pipe June 3 in order to attach a containment device -- are more than double the previous estimate of 12,000 to 19,000 barrels per day.

US Coast Guard Admiral Thad Allen, who is overseeing response to the worst oil spill in US history, said the containment device captured more than 15,000 barrels in the 24 hours ending midnight Wednesday.

There were fears before the pipe was cut that the operation could increase the flow by up to 20 percent although Interior Secretary Ken Salazar told a congressional hearing Wednesday it was probably between four and five percent.