Article Photos: Fracking for natural gas being powered by it, too 7/7

In this photo made on Thursday, Jan. 17, 2013, Universal Well Service fracturing engineering team leader Mike Michaelson, right, talks with technician Sean Cline  before they start the 16 cylinder diesel engine that has been converted to run on a blend of diesel and natural gas at the Cummins Bridgeway facility in Gibsonia, Pa. Oil- and gas-field companies from Pennsylvania to Texas are experimenting with converting the huge diesel engines that operate pumps that propel millions of gallons of water, sand and chemicals down a well bore in the fracturing process to break apart rock or tight sands that trap natural gas. (AP Photo/Keith Srakocic)