This paper compares the relative safety risks of four types of vehicle fuels. The fuels considered are hydrogen, natural gas, liquified petroleum gas (LPG), and gasoline. The accident scenario considered is a vehicle parked in a single-car garage for 2 h with a fuel-line leak. The comparison is made on the basis of the volume of combustible gas produced by each fuel. Only LPG and gasoline produced appreciable volumes of combustible gas.