Propane as an Alternative Fuel

The interest in propane (also known as liquefied petroleum gas or LPG) as an alternative transportation fuel stems mainly from its domestic availability, high energy density, and clean-burning qualities. It is the most commonly used alternative transportation fuel and the third most used vehicle fuel, behind gasoline and diesel. Propane is considered an alternative fuel under the Energy Policy Act of 1992.

Propane sold as vehicle fuel can be a mixture of propane with smaller amounts of other gases. According to the Gas Processors Association's HD-5 specification for propane as a transportation fuel, it must consist of 90% propane, no more than 5% propylene, and 5% other gases, primarily butane and butylene.

Propane is a gas at normal temperatures and pressures. It is stored onboard a vehicle in a tank pressurized to around 300 pounds per square inch—about twice the pressure as in an inflated truck tire. Under this pressure, propane becomes a liquid with an energy density 270 times greater than the gaseous form. A gallon of propane has about 25% less energy than a gallon of gasoline.

Because propane is transformed into a gaseous state before it is burned in an internal combustion engine, the engine runs more efficiently in low-speed, light-throttle conditions. The introduction of Liquid Propane Injection engines promises higher fuel efficiency.

See Propane Fueling Station Locations to find fueling stations near you. For price information, see the Alternative Fuel Price Report.