Propane, also known as liquefied petroleum gas (LPG) or propane autogas, has been used worldwide as a vehicle fuel for decades. LPG is propane, butane or a mixture of the two.
It is stored as a liquid, and propane fueling infrastructure is widespread. According to the Propane Education & Research Council, there are nearly 60,000 on-road propane vehicles with certified fuel systems in the United States. Many are used in fleet applications, such as school buses, shuttles and police vehicles. Propane vehicles are available from original equipment manufacturers (OEMs) or via a conversion.
Because a gallon of propane has 27% less energy than a gallon of gasoline, the fuel economy of propane vehicles is slightly lower; however, propane has a higher-octane rating than gasoline (104–112 compared to 87–92 for gasoline). This can result in improved performance and fuel economy over non-optimized engines.
The potential for lower maintenance costs is one reason behind propane's popularity for use in light- and medium-duty vehicles, such as trucks and taxis, and for heavy-duty vehicles, such as school buses. Engine life may be longer, and propane performs well in cold weather climates because the fuel’s mixture (propane and air) is completely gaseous when it enters the injection system and engine.