Lexikon

called also octane rating, a value used to indicate the resistance of a motor fuel to knock, measure of the ignition quality of gas (gasoline or petrol). octane numbers are based on a scale on which isooctane is 100 (minimal knock) and n-heptane is 0 (bad knock). A gasoline with an octane number of 98 has the same knock as a mixture of 98% isooctane and 2% n-heptane.