An octane rating, or octane number, is a standard measure of an engine or aviation gasoline capability against compression. The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates gasoline's capability against compression. In broad terms, fuels with a higher octane rating are used in higher-compression gasoline engines that potentially yield higher power. Note that such higher power comes from the fuel's higher compression by the engine, and not necessarily from the gasoline.