Propane is a by-product of natural gas and petroleum, occurring naturally during domestic oil refining and natural gas processing. It is 270 times more compact as a liquid than as a gas, making it highly economical to store and transport. Propane is also known as liquefied petroleum gas (LPG or LP gas). When used as an on-road engine fuel, it is called propane autogas.
The following articles give more information about propane: