The use of copolymers obtainable by - in a first reaction step copolymerizing at least one ethylenically unsaturated mono- or dicarboxylic acid or derivatives thereof, selected from the group consisting of - anhydrides in monomeric or polymeric form, - mono- or dialkyl esters, and - mixed esters, at least one α-olefin having from at least 16 up to and including 28 carbon atoms, optionally at least one further aliphatic or cycloaliphatic olefin which has at least 4 carbon atoms and is different than and optionally one or more further copolymerizable monomers other than monomers, and, selected from the group consisting of (Da) vinyl esters, (Db) vinyl ethers, (Dc) (meth)acrylic esters of alcohols having at least 5 carbon atoms, (Dd) allyl alcohols or ethers thereof, (De) N-vinyl compounds selected from the group consisting of vinyl compounds of heterocycles containing at least one nitrogen atom, N-vinylamides or N-vinyllactams, (Df) ethylenically unsaturated aromatics, (Dg) α,β-ethylenically unsaturated nitriles, (Dh) (meth)acrylamides and (Di) allylamines, followed by - in a second optional reaction step partly or fully hydrolyzing anhydride or carboxylic ester functionalities present in the copolymer obtained from to obtain a copolymer having a weight-average molecular weight Mw (determined by gel permeation chromatography with tetrahydrofuran and polystyrene as standard) of 1.5 to 4 kDa, the second reaction step being run at least when the copolymer obtained from reaction step does not comprise any free carboxylic functionalities, as corrosion inhibitors in diesel fuels or gasoline fuels having a content of alkali metals and/or alkaline earth metals and/or zinc of at least 0.1 ppm by weight. - in a first reaction step copolymerizing at least one ethylenically unsaturated mono- or dicarboxylic acid or derivatives thereof, selected from the group consisting of - anhydrides in monomeric or polymeric form, - mono- or dialkyl esters, and - mixed esters, at least one α-olefin having from at least 16 up to and including 28 carbon atoms, optionally at least one further aliphatic or cycloaliphatic olefin which has at least 4 carbon atoms and is different than and optionally one or more further copolymerizable monomers other than monomers, and, selected from the group consisting of (Da) vinyl esters, (Db) vinyl ethers, (Dc) (meth)acrylic esters of alcohols having at least 5 carbon atoms, (Dd) allyl alcohols or ethers thereof, (De) N-vinyl compounds selected from the group consisting of vinyl compounds of heterocycles containing at least one nitrogen atom, N-vinylamides or N-vinyllactams, (Df) ethylenically unsaturated aromatics, (Dg) α,β-ethylenically unsaturated nitriles, (Dh) (meth)acrylamides and (Di) allylamines, followed by at least one ethylenically unsaturated mono- or dicarboxylic acid or derivatives thereof, selected from the group consisting of - anhydrides in monomeric or polymeric form, - mono- or dialkyl esters, and - mixed esters, - anhydrides in monomeric or polymeric form, - mono- or dialkyl esters, and - mixed esters, at least one α-olefin having from at least 16 up to and including 28 carbon atoms, optionally at least one further aliphatic or cycloaliphatic olefin which has at least 4 carbon atoms and is different than and optionally one or more further copolymerizable monomers other than monomers, and, selected from the group consisting of (Da) vinyl esters, (Db) vinyl ethers, (Dc) (meth)acrylic esters of alcohols having at least 5 carbon atoms, (Dd) allyl alcohols or ethers thereof, (De) N-vinyl compounds selected from the group consisting of vinyl compounds of heterocycles containing at least one nitrogen atom, N-vinylamides or N-vinyllactams, (Df) ethylenically unsaturated aromatics, (Dg) α,β-ethylenically unsaturated nitriles, (Dh) (meth)acrylamides and (Di) allylamines, (Da) vinyl esters, (Db) vinyl ethers, (Dc) (meth)acrylic esters of alcohols having at least 5 carbon atoms, (Dd) allyl alcohols or ethers thereof, (De) N-vinyl compounds selected from the group consisting of vinyl compounds of heterocycles containing at least one nitrogen atom, N-vinylamides or N-vinyllactams, (Df) ethylenically unsaturated aromatics, (Dg) α,β-ethylenically unsaturated nitriles, (Dh) (meth)acrylamides and (Di) allylamines, - in a second optional reaction step partly or fully hydrolyzing anhydride or carboxylic ester functionalities present in the copolymer obtained from to obtain a copolymer having a weight-average molecular weight Mw (determined by gel permeation chromatography with tetrahydrofuran and polystyrene as standard) of 1.5 to 4 kDa, the second reaction step being run at least when the copolymer obtained from reaction step does not comprise any free carboxylic functionalities,