Propane is a three-carbon alkane, normally a gas, but compressible to a transportable liquid. It is derived from other petroleum products during oil or natural gas processing. It is commonly used as a fuel for engines, barbecue grills and home heating systems.
When used as vehicle fuel, it is commonly known as liquified petroleum gas (LPG or LP-gas), which can be a mixture of propane along with small amounts of propylene, butane, and butylene. The odorant ethanethiol is also added so that people can easily smell the gas in case of a leak.
Propane is also being used increasingly for vehicle fuels. In the United States, 190,000 on-road vehicles use propane, and 450,000 forklifts use it for power. It is the third most popular vehicle fuel in America, behind gasoline and diesel. In other parts of the world, propane used in vehicles is known as autogas. About 9 million vehicles worldwide use autogas.
The advantage of propane is its liquid state at a moderate pressure. This allows fast refill times, affordable fuel tank construction, and ranges comparable to gasoline. Meanwhile it is noticeably cleaner both in handling, and in combustion, results in less engine wear due to carbon deposits without diluting engine oil often extending oil-change intervals. However, public filling stations are still rare. Many converted vehicles have provisions for topping off from "barbecue bottles". Purpose-built vehicles are often in commercially-owned fleets, and have private fueling facilities.