WILLISTON, ND – JULY 23: A line of trucks drives past a gas flare on July 23, 2013 outside Watford City, North Dakota. Gas flares are created when excess flammable gases are released unexpectedly by pressure release valves during the drilling for oil and natural gas. North Dakota has been experiencing an oil boom in recent years, due in part to new drilling techniques including hydraulic fracturing and horizontal drilling. In April 2013, The United States Geological Survey released a new study estimating the Bakken formation and surrounding oil fields could yield up to 7.4 billion barrels of oil, doubling their estimate of 2008, which was stated at 3.65 billion barrels of oil. (Photo by Andrew Burton/Getty Images)