Novel fuels for gasoline engines comprise a synergistic mixture of a detergent additive component (A) and a synthetic carrier oil component (B), i) the detergent additive component (A) comprising at least one compound having a basic nitrogen atom which is substituted by a hydrocarbyl radical having a number average molecular weight of from about 500 to 1 300, and the detergent additive component (A) being contained in the fuel in an amount of from about 30 to 180 ppm by weight; and ii) the carrier oil component (B) comprising at least one compound of the following formula I R--O-(A-O).sub.x--H (I) where R is a straight-chain or branched C.sub.6-C.sub.18-alkyl group; A is a C.sub.3- or C.sub.4-alkylene group; and x is an integer from 5 to 35; the carrier oil component (B) being contained in the fuel in an amount of from about 10 to 180 ppm by weight.