is an expression of the antiknock properties of an aviation gasoline with a Motor Octane Number higher than 100. The laboratory procedure for determining performance number is the same as that for Motor Octane Number (see octane number), except that performance number is based on the number of milliliters of tetraethyl lead (see lead alkyl) in the reference isooctane blend that matches the antiknock characteristics of the test fuel. A 100/130 grade aviation gasoline has an octane number of 100 at lean fuel mix and a performance number of 130 at rich mix.

Also see lean and rich octane numbers.