This paper describes the properties of synthetic water-soluble polymers that are stable for extended periods of time in hard brines at very high temperatures. Several copolymers of vinylpyrrolidone (VP) and acrylamide (AM) were prepared and evaluated in our laboratories for EOR application in hostile environments. VP in the copolymer composition protects AM against extensive thermal hydrolysis, which otherwise will result in loss of viscosity and precipitation. A range of VP/AM copolymer compositions was found to tolerate the harsh conditions of 250°F [121 °C] in seawater for extended periods of time and to be suitable for EOR application under these conditions. The performance of these polymers in porous media was evaluated by extensive coreflood experiments in Berea sandstone at 250°F [121 °C] with synthetic seawater. The results indicate that these copolymers can easily be injected into porous media and that they can be effective polymers for EOR application in hostile environments.