Spare Fuel (Six Half Gallon) - The Original Storable and Safe Emergency Fuel for Gas Engines Spare Fuel keeps you prepared if you run out of gas along the highway. Spare Fuel is patented emergency fuel for any gas-powered (non-diesel) engine. Spare Fuel is safe to store in your vehicle's trunk or storage bay for years. Spare Fuel works in gas-powered cars, trucks, boats, generators, and more. Spare Fuel is the original fuel product designed to keep you prepared.