With pump trucks aplenty, workers at hydraulic fracturing sites have been able to extract petroleum and natural gas from subterranean shale. The plentiful and cheap energy has given the U.S. a competitive edge. (Associated Press)

With pump trucks aplenty, workers at hydraulic fracturing sites have been able to extract petroleum and natural gas from subterranean shale. The plentiful and cheap energy has given the U.S. a competitive edge. (Associated Press)