Liquified petroleum gas (LPG) broadly referred to as commercial propane, commercial butane, and mixtures of the two. LPG is derived from two sources: natural gas processing and petroleum refining. Produced by either one of them, LPG is a bi- product. The name LPG is explained by the fact that the gas assumes a liquid state at precious of 2 to 20 bar; the actual value depends upon the propane-butane ratio. The composition of commercial LPG varies greatly from 1 country to another. In the United states, automatic LPG generally contains more than 85% propane. In Europe on the other hand LPG contains nearly equal parts of propane and butane.