A gasoline fuel composition comprising a major portion of gasoline and a minor portion of one or more polyaryl amines, effective to increase the octane number of the gasoline composition, represented by the formula: ##STR1## where R.sup.1 -R.sup.5 are independently hydrogen or C.sub.1 -C.sub.8 aliphatic hydrocarbons; R.sup.6 -R.sup.8 are independently hydrogen or C.sub.1 -C.sub.6 aliphatic hydrocarbons; x is between 0 and about 2, inclusive, y is between 0 and about 3, inclusive; and z is between about 1 and about 50, inclusive.