Liquefied petroleum gas (LPG) is a flammable mixture of hydrocarbon gases used as a fuel in vehicles (and heating appliances). It is also sometimes called GPL, LP Gas, autogas, or liquid propane gas. It is used more frequently as a replacement for chlorofluorocarbons in refrigerants.
Common varieties of LPG includes mixes that are mostly propane. mostly butane, and a mixture of both propane and butane.
LPG was introduced to the market as a "clean-burning" fuel. It reduce emissions of carbon monoxide compared to gasoline engines (but not as low as in diesel engines).