Of all the alternatives to gasoline from petroleum, methane is the one source that could displace much of it relatively rapidly. For example, shale oil in quantity is decades away, as are liquid fuels from coal. But methane is available and conversion of cars to use it is not difficult. At the moment, proved reserves of natural gas are limited, but the National Petroleum Council and the American Gas Association are confident that much more will be found and tapped. They point to methane in the Devonian shales of the Appalachian Basin, to methane associated with coal, and to natural gas in western tight gas sands. In addition, many other horizons have not been explored. Once successful wells are drilled, processing equipment can be quickly installed and the production channeled into the pipeline network. Thus, the nation has an answer to a prolonged attenuation of oil imports. The earth's crust contains large amounts of methane. The gas can also be obtained from biomass and from synthesis gas derived from coal. In the United States, a million-mile pipeline network exists for distribution of the gas. Methane is already being used in about 400,000 vehicles around the world, including 250,000 in Italy and 20,000 to 30,000 in the United States. Users have found that engine wear is reduced: lubricating oil is not diluted as it is when gasoline is used. Exhaust gases are relatively nonpolluting. Start-up of motors is not affected by cold weather. An engine designed especially for methane has an energy efficiency greater than that of ordinary automobiles. Conventional cars and trucks can be modified at a cost of $1500 to burn either methane or liquid fuels. When they burn methane, such engines are about 10 percent less efficient and, for the same piston displacement, generates 25 percent less power than with gasoline.