Projections of the world's petroleum supply point to acute shortages by the end of this century which could impair air transportation. Synthetic fuels will undoubtedly be needed to relieve this shortage. One form of synthesized fuel will be liquid methane, which can be manufactured from any of the hydrocarbon sources such as coal, shale, biomass, and organic waste. Because there are so many potential sources of this fuel, including natural and synthetic sources, it should be considered as a petroleum replacement. In this paper a simple cycle analysis is carried out for a turboprop engine flying at Mach 0.8 and 10,688 meters (35,000 ft.) altitude. Cycle performance comparisons are rendered for four cases in which the turbine cooling air is cooled or not cooled by the methane fuel. The advantages and disadvantages of involving the fuel in the turbine cooling system are discussed. Methane combustion characteristics are appreciably different from Jet A and will require different combustor designs. Although a number of similar difficult technical problems exist, a highly fuel efficient turboprop engine burning methane appears to be feasible.