propane, CH3CH2CH3, colorless, gaseous alkane. It is readily liquefied by compression and cooling. It melts at - 189.9°C and boils at - 42.2°C. Propane occurs in nature in natural gas and (in dissolved form) in crude oil; it is also a byproduct of petroleum refining. It is used chiefly as a fuel. For this purpose it is sold compressed in cylinders of various sizes, often mixed with other hydrocarbons, e.g., butane. Propane fuel is used in a type of cigarette lighter and in portable stoves and lamps.