Liquefied petroleum gas (LPG) is a mixture of hydrocarbon fuels stored in pressurised vessels in liquid form. It is mostly derived from fossil fuel sources and consists most commonly of a mixture of propane and butane. The specific combination can vary from mostly propane to mostly butane. LPG is highly flammable and used as fuel in internal combustion engine vehicles (ICEVs), generators, and heating and cooking appliances.
In the automotive industry, LPG is often called autogas. It is the third most popular fuel in the world. Vehicles using LPG emit 15% less CO2 than vehicles using petrol. Autogas is commonly used in buses, trucks, and cars. There are manufactured LPG vehicles, but it is also popular to add an LPG system to ICEVs afterwards. In recent years, however, LPG is losing its popularity to compressed natural gas (CNG) which is safer and releases less greenhouse gas when burned.