Octane Number

Key Points about Octane Number

Higher Octane Number  -  Indicates that the fuel can withstand greater compression before detonating.  Higher octane fuels are often used in high-performance or high-compression engines to prevent knocking.
Lower Octane Number  -  Means the fuel is more prone to knocking, which can be problematic in high-compression engines but is generally suitable for low-compression engines.

Common Octane Numbers

• 87  -  Regular gasoline, suitable for most standard engines.
• 89–90  -  Mid-grade gasoline.
• 91–94  -  Premium gasoline, used for high-performance or luxury vehicles.

Measurement

The octane number is determined by comparing the fuel's performance to a mixture of iso-octane (which resists knocking) and n-heptane (which knocks easily).  For example, a fuel with an octane rating of 90 performs similarly to a blend of 90% iso-octane and 10% n-heptane.