Associated Press

The government estimates up to 4.3 billion barrels of oil can be recovered from the Bakken shake formation in North Dakota and Montana, using current technology.

The U.S. Geological Survey calls it the largest continuous oil accumulation it has ever assessed.

The Bakken Formation encompasses some 25,000 square miles in North Dakota, Montana, Saskatchewan and Manitoba. About two-thirds of the acreage is in western North Dakota, where the oil is trapped in a thin layer of dense rock nearly two miles beneath the surface.

The report released today by USGS was done at the request of Sen. Byron Dorgan, D-N.D., over the past 18 months.