The octane number is determined by comparing, under standard conditions, the knock intensity of the fuel with that of blends of two reference fuels: iso-octane, which resists knocking, and heptane, which knocks readily.

How is octane number increase?

Octane number of fuels can be improved by addition of oxygenates such as ethanol, MTBE (methyl tert-butyl ether), TBF (tertiary butyl formate) and TBA (tertiary butyl alcohol) as well as their blends with gasoline that reduce the cost impact of fuels.

What is a good octane number?

Most auto manufacturers recommend 87 octane gasoline, but advise using a higher octane gasoline if knocking is an issue with the lower grade.