A massive oil field underneath Montana and the Dakotas that has the potential to revolutionize America's energy needs could in fact contain twice as much oil as previously thought.

The United States Geological Survey sent out an updated estimate for how much oil is contained in the so-called Bakken field, a giant underground reservoir under South Dakota, North Dakota and Montana.

The USGS now says there is 7.4 billion barrels of technically recoverable oil in the Bakken and Three Forks formations.

That's more than twice as much as the USGS was forecasting for the field as recently as 2008, when they said there was probably 3.6 billion barrels of oil.

"These world-class formations contain even more energy resource potential than previously understood, which is important information as we continue to reduce our nation's dependence on foreign sources of oil," Interior Secretary Sally Jewell said of the updated estimate.

Since the 2008 estimate, more than 4,000 wells have been drilled in the Williston Basin, providing updated subsurface geologic data.

Previously, the Three Forks Formation was thought to be unproductive, but new drilling techniques resulted in a new understanding of the reservoir and its resource potential, the USGS said in a release.

The formations also likely contain 6.7 trillion cubic feet of undiscovered, technically recoverable natural gas, the USGS said.

The U.S. currently uses almost 20 million barrels of oil per day, and U.S. President Barack Obama says he would like to see America become energy self-sufficient within a decade.

Canada exports more than three million barrels of crude per day, a figure that may well increase exponentially if TransCanada's Keystone XL pipeline to ship Canadian bitumen to refineries on the U.S. Gulf Coast comes to pass.