In this July 26, 2011, file photo, a worker hangs from an oil derrick outside of Williston, N.D. State data show that 1 billion barrels of oil have been produced from the rich Bakken shale formation in western North Dakota and eastern Montana. Data show that North Dakota has tallied 852 million barrels of Bakken crude, and Montana has produced about 151 million barrels. (AP Photo/Gregory Bull, File)