Quaternary ammonium salts additives for fuels

The use of a quaternary ammonium salt additive in a gasoline composition to improve the performance of a gasoline engine when using said gasoline composition, wherein the quaternary ammonium additive comprises one or more quaternary ammonium salt(s) formed by the reaction of a compound of formula (A): and a compound formed by the reaction of a hydrocarbyl-substituted acylating agent and an amine of formula (B1) or (B2): wherein R is an optionally substituted alkyl, alkenyl, aryl or alkylaryl group; R1 is an alkyl, aryl or alkylaryl group having up to 36 carbon atoms; Rand Rare the same or different alkyl groups having from 1 to 36 carbon atoms; X is an alkylene group having from 1 to 20 carbon atoms; n is from 0 to 20; m is from 1 to 5; and Ris hydrogen or a Cto Calkyl group.