Yet alternative fuels for aviation are hard to come by. The Air Force says it's open to all sources of power for its fleet, but according to former assistant secretary of the Air Force William Anderson, petroleum, natural gas and coal are our only current options—and when you look at the U.S.'s resources, the choice is clear. "We're not the largest holder of oil reserves, so that's not a good option," he says. "We're not the biggest holder of natural gas. But we are the Saudi Arabia of coal." So the Air Force is doing its best to spark a domestic fuel industry that would be devoted, most likely, to digging new coal mines and building the country's first major coal-to-liquids (CTL) plants. To make the market bigger, it wants to convince the other branches of the military and even domestic airlines to run their fleets on liquefied coal, too.