Liquified petroleum gas (LPG) is a mixture of hydrocarbons mostly propane and butane, with formulae C₃H₈ and C₄H₁₀, respectively. In large concentrations LPG may cause asphyxiation. Examples of LPG are propane, n-butane and isobutane.
In addition to any LPG mixture there is always an odorant so that a leakage can be discovered. Often the odorant is a terribly smelling thiol, an organic molecule with a --SH group which has a very low threshold for human detection (on the level of ppb, parts per billion). Liquified petroleum gas is extremely flammable and thus suitable for burners, heating appliances, and vehicles. Also, it is used as aerosol propellants and as refigrerants instead of freons.