Propane, or liquefied petroleum gas (LPG), is the world’s third most common transportation fuel, behind all gasoline and diesel. Propane has a higher octane rating than gasoline, so it can be used with higher engine compression ratios and is more resistant to engine knocking. However, it takes more fuel by volume than regular gasoline to drive the same distance.

Propane accounts for about 2% of the energy used in the United States, according to the DOE. Of that, less than 3% is used for transportation. Most LPG used in transportation vehicles is used in government and private-sector fleets.

Propane is stored under pressure inside a tank. As pressure is released, the liquid propane vaporizes and turns into gas that is used in combustion. If spilled, propane doesn’t harm soil, surface water or ground water. Propane is used mainly for home and water heating, cooking, grilling and refrigerating food, clothes drying and powering farm and industrial equipment. The chemical industry also uses propane as a raw material for making plastics and other compounds.