Fracking for natural gas

In this Jan. 17, 2013, photo, technician Sean Cline finishes up the conversion of a 50 litre, 16 cylinder, Cummins diesel engine with four turbo-chargers that has been converted to run on a blend of diesel and natural gas at the Cummins Bridgeway facility in Gibsonia, Pa.

Credit: AP Photo/Keith Srakocic