Current studies of geologic storage of CO2, with the exception of CO2 sequestration in coal beds, focuses on supercritical CO2, emphasizing the stability of the fluid, solubility of CO2 in saline formation water and miscibility with crude oil. Likewise, with the exception of very early research, the use of CO2 to enhance oil recovery (EOR) historically focused on supercritical CO2 to achieve miscible conditions with crude oil. The only possibility of liquid CO2 geologic storage is in formations with temperatures less than the critical temperature of CO2. Due to the naturally occurring geothermal temperature gradient, most all geologic formations currently considered for CO2 sequestration and EOR exceed the TcCO2. A research plan has been developed to investigate the use of depleting (mature) oil reservoirs with formation temperatures less than critical temperature of CO2 to sequester liquid CO2 and investigate the implications of EOR from the liquid CO2 displacement process. Relatively higher pressures are required to attain liquid CO2, which translate to fracture gradients as high as 1.0 psi/ft. However, fracture stimulation data published in early literature and field data from fracture stimulation companies in the Illinois Basin show that fracture gradients of up to 1.0 psi/ft are commonly recorded in the shallower producing horizons of the Basin. Therefore, the pressure requirement may not be a detriment. Because of the liquid/gas phase changes and consequent changes in density and viscosity of CO2 at subcritical temperatures, low temperature oil reservoirs provide a unique opportunity for liquid CO2 storage and the application of a novel and innovative EOR-CO2 cyclic multi-reservoir displacement process within the Illinois Basin.