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.