Liquefied petroleum gas (LPG) is an alternative fossil fuel that can be extracted from crude oil or processed from natural gas purification. It is primarily a mixture of hydrocarbon gases like propane and butane, which exist as gases at normal room temperature and atmospheric pressure. Safe storage properties and portability of this gas adds to its popularity.
At normal temperature and pressure, LPG usually evaporates and thus is supplied in liquefied form in 200 psi (pounds per square inch) pressurized containers. These containers are filled only up to 80-85% of their capacity to allow for thermal expansion of the liquefied gas, as its volume changes on vaporization.