The octane number provides a measure of the amount of compression a fuel can undergo before it combusts. The name “octane rating” comes from the fact that isooctane is used as the standard against which a fuel’s compression characteristics are measured. A fuel with an octane rating of 89 means that it has the same ability to withstand compression as a mixture of 89% isooctane and 11% heptane. In reality, gasoline contains many other components. Fuels with higher octane ratings are typically used in higher performance automobiles. Since fuels may be able to withstand compression better than isooctane, it’s entirely possible to achieve octane ratings of over 100.