The use of copolymers obtainable by - in a first reaction step copolymerizing at least one ethylenically unsaturated mono- or dicarboxylic acid or derivatives thereof, preferably a dicarboxylic acid, where the derivatives are - the relevant anhydrides in monomeric or else polymeric form, - mono- or dialkyl esters, or - mixed esters, at least one α-olefin having from at least 12 up to and including 30 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 reaction step partly or fully reacting anhydride or carboxylic acid functionalities present in the copolymer obtained from with at least one compound having at least one alcohol group or amino group and at least one carboxylic acid group, and - in a third reaction step hydrolyzing the anhydride functionalities present in the copolymer obtained from, as fuel additive or lubricant additive, especially diesel fuel additive. - in a first reaction step copolymerizing at least one ethylenically unsaturated mono- or dicarboxylic acid or derivatives thereof, preferably a dicarboxylic acid, where the derivatives are - the relevant anhydrides in monomeric or else polymeric form, - mono- or dialkyl esters, or - mixed esters, at least one α-olefin having from at least 12 up to and including 30 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 reaction step partly or fully reacting anhydride or carboxylic acid functionalities present in the copolymer obtained from with at least one compound having at least one alcohol group or amino group and at least one carboxylic acid group, and - in a third reaction step hydrolyzing the anhydride functionalities present in the copolymer obtained from, as fuel additive or lubricant additive, especially diesel fuel additive. at least one ethylenically unsaturated mono- or dicarboxylic acid or derivatives thereof, preferably a dicarboxylic acid, where the derivatives are - the relevant anhydrides in monomeric or else polymeric form, - mono- or dialkyl esters, or - mixed esters, - the relevant anhydrides in monomeric or else polymeric form, - mono- or dialkyl esters, or - mixed esters, at least one α-olefin having from at least 12 up to and including 30 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, - in a second reaction step partly or fully reacting anhydride or carboxylic acid functionalities present in the copolymer obtained from with at least one compound having at least one alcohol group or amino group and at least one carboxylic acid group, and - in a third reaction step hydrolyzing the anhydride functionalities present in the copolymer obtained from,