Propane is a three-carbon alkane with the molecular formula C3H8, normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central heating. Propane is one of a group of liquefied petroleum gases. The others include butane, propylene, butadiene, butylene, isobutylene and mixtures thereof.

Propane was first identified as a volatile component in gasoline by Walter O. Snelling of the U.S. Bureau of Mines in 1910. The volatility of these lighter hydrocarbons caused them to be known as "wild" because of the high vapor pressures of unrefined gasoline. On March 31, the New York Times reported on Snelling's work with liquefied gas and that "...a steel bottle will carry enough gas to light an ordinary home for three weeks.

The density of liquid propane at 25 °C (77 °F) is 0.493 g/cm3, which is equivalent to 4.11 pounds per U.S. liquid gallon. Propane expands at 1.5% per 10 °F. Thus, liquid propane has a density of approximately 4.2 pounds per gallon at 60 °F.

As of November 2011, the retail cost of propane was approximately US$2.825 per gallon, or roughly $30.82 per 1 million BTUs.