NOVELTY - Fuel and lubricant additive comprises a portion of at least one reaction products comprising quaternized nitrogen compound or a partial fraction of quaternized nitrogen compound obtained from the reaction product by purification, where the reaction product is produced by the method comprising reacting at least one hydrocarbylepoxide (I) with at least one tertiary amine compound (II) in the presence of at least one acid.    USE - The fuel and lubricant additive is useful: for reducing or preventing deposits in the injection systems such as common-rail injection systems of direct-injection diesel engines, for reducing fuel consumption of direct-injection diesel engines, preferably diesel engines having common-rail injection systems, and for minimizing the power loss in direct-injection diesel engines, preferably in diesel engines having common-rail injection systems; and as diesel fuels, biodiesel fuels, petrol, and alkanol-containing gasoline fuels, where the additive is useful as a gasoline fuel additive, a diesel fuel additive, and a detergent additive, and for gasolines for the operation of DISI engines (all claimed).    ADVANTAGE - The fuel and lubricant additive improves performance of the diesel engines with reduced fuel consumption.    DETAILED DESCRIPTION - Fuel and lubricant additive comprises a portion of at least one reaction products comprising quaternized nitrogen compound or a partial fraction of quaternized nitrogen compound obtained from the reaction product by purification, where the reaction product is produced by the method comprising reacting at least one hydrocarbylepoxide of formula (I) with at least one tertiary amine compound of formula (Ra1Rb1Rc1N) (II) in the presence of at least one acid comprising saturated or unsaturated, aliphatic or aromatic 1-20C monocarboxylic acids and fatty acids comprising linear or branched, mono-or polyunsaturated, optionally substituted 6-30C mono-carboxylic acids.    R1, R2 = linear or branched long-chain hydrocarbyl (optionally saturated);    R3, R4 = H or short-chain hydrocarbyl; either    Ra1-Rc1 = linear or branched, optionally saturated hydrocarbyl; or    two of Ra1, Rb1, Rc1+N = 5 - to 7-membered non-aryl or aryl heterocyclic ring, which optionally forms at least one further ring heteroatom such as O, S or N.    INDEPENDENT CLAIMS are included for:    (1) the quaternized nitrogen compound comprising the reaction product;    (2) producing the quaternized nitrogen compound, comprising the step as per above se;    (3) use of the reaction product comprising the quaternized nitrogen compound, as fuel or lubricant additive, where the reaction product is obtained by the method comprising the steps as per above se in the presence of at least one acid compound of formula (H+A-) (IV); and    (4) an additive concentrate comprising the quaternized nitrogen-containing compound in combination with other diesel or gasoline fuel additives or lubricant additive.    A- = anion of at least one monovalent or polyvalent inorganic or organic, natural or synthetic acid.