A high molecular weight (> 10(6)) copolymer of NN-dimethyl acrylamide with Na-2-acrylamido-2-methylpropanesulfonate (NNDAM-NaAMPS) was prepared and characterized. The efficacy of the copolymer as an enhanced oil recovery (EOR) chemical was studied. Core flood tests using 72-150 mesh size unconsolidated sand having a porosity of 42% were carried out at different brine concentrations and temperatures. Initially, a crude oil fraction (150-300degreesC) and, finally, the crude itself were used as the oils to be recovered. The copolymer was brine compatible. After a water flood, about 5.6% original oil in place (OIP) could be recovered by injecting 2000 ppm polymer solution to the sand pack containing oil fraction and 5000 ppm NaCl brine. The polymer solution was found to be thermally stable at 120degreesC at least for a period of 1 month. It was further confirmed that the residual oil recovery increased with the increase of temperature. About 11% of OIP could be recovered as additional oil by injecting a 2000 ppm polymer solution to the unconsolidated sand pack containing one of the Indian crude oils and brine consisting of mono-and bivalent metal ions at 90degreesC.