
An oil drilling rig stands on the Bakken formation in Watford City, North Dakota, U.S., on Friday, Oct. 14, 2011. Oil production in the state has tripled in five years, attracting the likes of Exxon Mobil Corp., and Norway's Statoil ASA, which agreed this week to pay $4.5 billion for Brigham Exploration Co., one of the companies that figured out how tap dense rock that the U.S. Geological Survey has estimated may contain 4.3 billion barrels of oil. The productive Bakken formation stretches from South Dakota into Canada's province of Saskatchewan. Photographer: Matthew Staver/Bloomberg
Matthew Staver/Bloomberg