Octane rating is used to represent the “antiknock” properties of fuel. The octane rating of a fuel is indicated on the pump—using numbers such as 87, 90, 91, etc. The higher the number, the greater the octane rating of the gasoline. The higher the octane rating, the slower the fuel burns—and the less likely your engine will knock. Ethanol, for example, adds two to three octane numbers when blended with ordinary gasoline—making it an octane-enhancer.