It's made from petroleum refining and natural gas processing. Propane is normally a gas, but it's stored in liquid form on a vehicle. Once the propane enters the engine, it becomes a gas again, which helps this fuel to burn so cleanly. The propane fuel grade used in vehicles is called HD-5.
Propane is widely available.
Hawaii has over 300 refueling sites throughout the islands. Propane fuel tanks are 20 times more puncture resistant than conventional gasoline tanks. Engines run by propane are cleaner and last longer. Propane vehicles can have as much as double the engine life of gasoline vehicles. Propane reduces lubricant contamination by fuel and has little to no carbon build up in combustion chambers or pistons.