The present invention relates to a composition comprising a first polymer and a second polymer, wherein the first polymer comprises repeating units derived from a monomer A which is selected from the group consisting of an alkyl ester of acrylic acid having at least 8 C-atoms, an alkyl ester of methacrylic acid having at least 9 C-atoms, and mixtures thereof, a monomer B which is an ethylenically unsaturated, polymerizable monomer having an acid group, and optionally at least one monomer C, wherein each monomer C is an ethylenically unsaturated, polymerizable monomer different from monomer A and different from monomer B, wherein the second polymer comprises repeating units derived from a monomer D which is selected from the group consisting of an alkyl ester of acrylic acid having at least 8 C-atoms, an alkyl ester of methacrylic acid having at least 9 C-atoms, and mixtures thereof, a monomer E which is an ethylenically unsaturated, polymerizable monomer having a basic group, and optionally at least one monomer F, wherein each monomer F is an ethylenically unsaturated, polymerizable monomer different from monomer D and different from monomer E. Furthermore, the present invention relates to a kit of parts comprising the said two polymers. Furthermore, the present invention relates to the use of the said composition or of the said kit of parts to increase the viscosity of an oil.
