This report presents the results of investigations to improve oil recovery using cosolvents in CO{sub 2} gas floods. Laboratory experiments were conducted to evaluate the application and selection of cosolvents as additives to gas displacement processes. A cosolvent used as a miscible additive changed the properties of the supercritical gas phase. Addition of a cosolvent resulted in increased viscosity and density of the gas mixture, and enhanced extraction of oil compounds into the CO{sub 2} rich phase. Gas phase properties were measured in an equilibrium cell with a capillary viscometer and a high pressure densitometer. A number of requirements must be considered in the application of a cosolvent. Cosolvent miscibility with CO{sub 2}, brine solubility, cosolvent volatility and relative quantity of the cosolvent partitioning into the oil phase were factors that must be considered for the successful application of cosolvents. Coreflood experiments were conducted with selected cosolvents to measure oil recovery efficiency. The results indicate lower molecular weight additives, such as propane, are the most effective cosolvents to increase oil recovery.