Octane number, a quality rating for Gasoline indicating the ability of the fuel to resist premature detonation and to burn evenly when exposed to heat and pressure in an Internal Combustion Engine. Premature detonation, indicated by knocking and pinging noises, wastes fuel and may cause engine damage. The octane number can be increased by varying the relative amounts of the different Hydrocarbons that make up the gasoline or by additives, e.g., tetraethyl lead. Federal regulations in the U.S. require commercial gasoline pumps to indicate the octane number, which is usually 87 or 89 for regular grade gasoline and 93 for premium grade. Since the early 1970s most Automobiles have been built to operate on low octane gasoline with little or no lead added.

This definition is in context to Explosive. See more contextual defintions for Octane Number.