Use of a water-swellable copolymer consisting essentially of the following monomers in polymerized forma) vinylpyrrolidone and/or methacrylamide (monomer A)；b) one or more monomers of the formula I R1-O-(CH2-CHR-O)n-R2 (I)wherein,R1 is a (meth)acrylic radical,R is H or CH3,R2 is a linear or branched C8 to C30 saturated hydrocarbon radical,n is an integer of from 5 to 100(monomer B)；c) vinylimidazole, quaternized vinylimidazole, N,N-dimethylaminopropyl-methacrylamide, quaternized N,N-dimethylaminoethyl (meth)acrylate, trimethylaminoethylmethacrylate chloride or a mixture of two or more thereof (monomer C)；d) (meth)acrylic acid and/or methyl(meth)acrylate (monomer D)；e) from 0 to 0.5% by weight of one or more cross-linkers (monomer E), based on the total weight of the monomers A to E,as a rheology-modifier in a formulation comprising at least one surfactant and/or an oil.
