Octane number, also called octane rating, is a measure of a fuel's ability to resist "knocking" or "pinging" during combustion in an internal combustion engine, particularly in gasoline engines. Knocking occurs when the air-fuel mixture in the engine's cylinder ignites prematurely or unevenly, which can lead to inefficient combustion and potential engine damage. The octane number is determined by comparing a fuel's performance to a mixture of two hydrocarbons: iso-octane (which has excellent resistance to knocking and is assigned an octane number of 100) and n-heptane (which knocks easily and is assigned an octane number of 0).
Octane Ratings (U.S.)
Regular Gasoline (87) - This is the standard fuel for most everyday vehicles in the U.S. RON is typically around 91–92, and MON around 82–83.
Mid-grade Gasoline (89) - A step up from regular, used in some vehicles that benefit from slightly higher knock resistance. RON might be around 93–94, MON around 84–85.
Premium Gasoline (91-94) - Common ratings include 91, 92, or 93 (varies by region and brand). Used in high-performance or luxury cars with higher compression engines.
High-Octane Fuels (100 or Higher) - Specialty fuels like 100-octane gasoline are used in aviation, racing, or extreme performance vehicles. Aviation gasoline (avgas) often has ratings like 100LL (low lead), with a RON around 100–104. Racing fuels can go even higher, like 110 or 120, depending on additives and formulation.
