The octane rating of a fuel is measured in octane numbers. The higher the number, the greater the fuel's ability to resist "knocking" or "pinging" during combustion, caused by the air/fuel mixture detonating prematurely in the engine. The most common type of rating is "Z". fuels with a Z rating have a compression ratio of at least 10.7:1. This means that for every 100 pounds of air that are burned, 97.