This paper deals with the commercial version of the spark-ignition engine. Methods are discussed whereby future engines may be increased in horsepower output and reduced in weight and size. Variable compression methods, charge stratification, fuel injection, and turbocharging are discussed as means of increasing engine output. Unconventional engines are discussed, but it is felt they do not have any appreciable application to commercial spark-ignition of the future. It is concluded that commercial spark-ignition of tomorrow will remain essentially as we know it today except that it will be more compact and will weigh less per horse-power or per cubic foot.