WASHINGTON, April 30 (Reuters) – 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.