Definition of octane number in English:

octane number

(also octane rating)

Pronunciation /ˈäkˌtān ˌnəmbər/ /ˈɑkˌteɪn ˌnəmbər/


  • A figure indicating the antiknock properties of a fuel, based on a comparison with a mixture of isooctane and heptane.

    ‘In particular, the formation of branched alkanes increases the octane number and combustibility of the resulting hydrocarbon.’
    • ‘Using a fuel of a higher octane rating than that recommended for your car doesn't improve its performance.’
    • ‘The higher the octane number you see on a gas pump, the more the fuel can be compressed before it explodes.’
    • ‘However, ethanol has a good octane rating of around 112 and a high heat-off evaporation so it cools down the intake charge.’
    • ‘Pyrolysis oil can also be added to gasoline to increase its octane rating.’