Toward the end of this century the shortfall of supply below demand of the products of natural crude oil will become severe. Research is already well under way to provide alternative fuels for spark-ignition engines which will be independent of natural crude oil. These include fuels from oil shales and tar sands, as well as synthetic fuels, alcohols, and gases; sources include coal, natural gas and biological origins. These fuels will cost two to three times as much in real terms as gasoline from oil does now, so an even stronger emphasis on fuel economy will be required. Most of these alternative fuels are more suited to the spark-ignition engine than the compression-ignition engine, and this paper predicts that the changeover to them will cause an increase rather than a decrease in the market penetration of the spark-ignition engine. It is concluded that the alternative fuel most likely to gain general acceptance is synthetic gasoline made from coal or natural gas, or in some areas from agricultural by-products.