Fracking for natural gas

In this Jan. 17, 2013, photo, Universal Well Services fracturing engineering team leader Mike Michaelson opens the cover of a display panel before he starts the 16 cylinder diesel engine for the first time since it was converted to run on a blend of diesel and natural gas at the Cummins Bridgeway facility in Gibsonia, Pa. Since there was no natural gas available at this facility, the engine would run on diesel fuel alone this day.

Credit: AP Photo/Keith Srakocic