Twice as Much Oil as Thought in North-Central United States

Billions of barrels more than previously estimated

An oil-rich region of the north-central United States holds more than twice the recoverable crude supplies estimated just five years ago, according to a government study that highlights the nation's march toward energy self-sufficiency.

The Bakken Formation and Three Forks Formation, which spans parts of Montana, North Dakota and South Dakota together hold an estimated 7.4 billion barrels of undiscovered, technically recoverable oil, the study released on Tuesday said.

That total is more than double the previous estimate, from 2008, and officials said it is a building block towards energy independence.