FILE PHOTO: A warning sign for a natural gas pipeline is seen in front of natural gas flares at an oil pump site outside of Williston, North Dakota March 11, 2013. REUTERS/Shannon Stapleton
FILE PHOTO: A warning sign for a natural gas pipeline is seen in front of natural gas flares at an oil pump site outside of Williston, North Dakota March 11, 2013. REUTERS/Shannon Stapleton