The adsorption behavior of poly(N,N-dimethylacrylamide-co-Na 2-acrylamido-2-methylpropanesulfonate), an enhanced oil recovery polymer, was studied. Adsorption isotherms show that adsorption on bentonite is very high followed by that on limestone that, in turn, is much higher than that on sand surface following the order: bentonite much greater than limestone > sand. On the addition of NaCl, adsorption on sand surface decreased to a minimum value and then increased. Adsorption increased with decreasing pH and also decreasing the content of Na 2-acrylamido-2-methylpropanesulfonate in the copolymer. The amount of the copolymer adsorbed on the sand surface is comparable to that of partially hydrolyzed polyacrylamide but much less than that of poly(acrylamide-co-vinylpyrrolidone). The type of adsorption was found to be physical, which is supported by the enthalpy of adsorption as well as by IR spectra. (C) 2003 Wiley Periodicals, Inc.