The present invention describes a polymer useful as viscosity index improver comprising units derived from one or more ethylenically unsaturated ester compounds of formula (I), where R is hydrogen or methyl, R1 means a linear, branched or cyclic alkyl residue with 1-6 carbon atoms, R2 and R3 independently represent hydrogen or a group of the formula —COOR′, where R′ means hydrogen or a alkyl group with 1-6 carbon atoms, units of one or more ethylenically unsaturated ester compounds of formula (II), where R is hydrogen or methyl, R4 means a 2-alkyl branched alkyl residue with 12-18 carbon atoms, R5 and R6 independently are hydrogen or a group of the formula —COOR″, where R″ means hydrogen or an alkyl group with 12-18 carbon atoms, and units of one or more ethylenically unsaturated ester compounds of formula (III), where R is hydrogen or methyl, R7 means a linear alkyl residue with 12-24 carbon atoms, R8 and R9 independently are hydrogen or a group of the formula —COOR″, where R″ means hydrogen or an alkyl group with 12-24 carbon atoms wherein said polymer comprises at least 10% by weight units derived from one or more ethylenically unsaturated ester compounds of formula (I), based on the total weight of the polymer, said polymer comprises at least 10% by weight units derived from one or more ethylenically unsaturated ester compounds of formula (II), based on the total weight of the polymer, and said polymer comprises at least 10% by weight units derived from one or more ethylenically unsaturated ester compounds of formula (III), based on the total weight of the polymer.