NOVELTY - A reaction product (P1) comprising a quaternized nitrogen compound or its fraction is obtained by a) reacting a hydrocarbyl-substituted polycarboxylic acid compound with a compound comprising oxygen or nitrogen group reactive, especially capable of addition or condensation, with the polycarboxylic acid, and comprising at least one quaternizable amino group, to obtain a quaternizable hydrocarbyl-substituted polycarboxylic acid compound, and b) converting the quaternizable amino group to a quaternary ammonium group by using a quaternizing agent.    USE - In the fuel composition selected from diesel fuels, biodiesel fuels, gasoline fuels and alkanol-containing gasoline fuels; as fuel additive; as additive for reducing the fuel consumption of direct-injection diesel engines, especially of diesel engines with common-rail injection systems, and/or for minimizing power loss in direct-injection diesel engines, especially in diesel engines with common-rail injection systems; as a gasoline fuel additive for reducing the level of deposits in the intake system of a gasoline engine, such as especially direct injection spark ignition (DISI) and port fuel injector (PFI) engines; as a diesel fuel additive, especially as a cold flow improver, as a wax antisettling additive (WASA) or as an additive for reducing the level of and/or preventing deposits in the intake systems, such as especially the internal diesel injector deposits (IDIDs), and/or valve sticking in direct-injection diesel engines, especially in common-rail injection systems (all claimed).    ADVANTAGE - The present reaction products as additives have low toxicity (caused by the specific selection of the quaternizing agent), burn ashlessly, exhibit a high content of quaternized product, allow an economic reaction regime in its preparation, and surprisingly have improved handling properties, such as especially improved solubility, such as especially in diesel performance additive packages. At the same time, the present reaction products as additives exhibit improved action with regard to prevention of deposits in diesel engines.    DETAILED DESCRIPTION - A reaction product (P1) comprising a quaternized nitrogen compound or its fraction is obtained by a) reacting a hydrocarbyl-substituted polycarboxylic acid compound with a compound comprising oxygen or nitrogen group reactive, especially capable of addition or condensation, with the polycarboxylic acid, and comprising at least one quaternizable amino group, to obtain a quaternizable hydrocarbyl-substituted polycarboxylic acid compound, and b) converting the quaternizable amino group to a quaternary ammonium group by using a quaternizing agent, where the quaternizing agent is the alkyl ester of a cycloaromatic or cycloaliphatic mono- or polycarboxylic acid, especially of a mono- or dicarboxylic acid, or of an aliphatic polycarboxylic acid, especially dicarboxylic acid. INDEPENDENT CLAIMS are included for the following:    (1) a fuel composition (C1) comprising in a majority of a customary fuel, a proportion of at least one reaction product comprising a quaternized nitrogen compound, or its fraction which comprises a quaternized nitrogen compound and is obtained from the reaction product by purification;    (2) preparing (P2) a quaternized nitrogen compound involving the reaction of a quaternizable hydrocarbyl-substituted polycarboxylic acid compound comprising at least one tertiary quaternizable amino group with a quaternizing agent which converts the at least one tertiary amino group to the quaternary ammonium group; and    (3) an additive concentrate comprising in combination with further diesel fuel or gasoline fuel additives, especially diesel fuel additives, at least one quaternized nitrogen compound prepared according to method (P1).