The Bakken shale formation, 10,000 feet beneath the Williston Basin, holds 4.3 billion barrels of oil, the Thursday report said.

The estimate includes what the USGS believes is recoverable using current technology.

The amount is also close to what a state survey, due April 28, will say is available, North Dakota geologist Ed Murphy told the Bismarck Tribune.

"We're in the same ballpark," Murphy said.

"This is very big news," Sen. Byron Dorgan, D-N.D., said during a teleconference with reporters Thursday, the Grand Forks Herald reported.

"I think there's going to be a lot more attention nationally and internationally to this region," Dorgan said.