Octane is a measure of the ignition quality of gasoline. The higher the octane number, the less susceptible the fuel is to “knocking.” Knocking occurs when the fuel prematurely burns in the engine’s combustion chamber due to compression – instead of being ignited by the spark as the engine is designed. The higher the octane number, the more compression the fuel can withstand before igniting. And ultimately, the more efficiently the engine performs.nEthanol naturally adds octane to gasoline and does so with a renewable, clean-burning and less expensive octane source. The higher the ethanol blend, the higher the octane rating. Straight ethanol has a 113 octane rating.