Starting from the original definition of the cohesive energy density and the Hildebrand solubility parameter, an approach utilizing an equation of state of the form P = f(rho,T) is used for calculating Hildebrand solubility parameters for a range of temperatures and pressures, including the supercritical fluid region. In addition, an approach is presented to determine Hansen solubility parameters over the same range of temperatures and pressures. The pure fluid used in these calculations is carbon dioxide (CO2). CO2 has been extensively studied, and its use as a supercritical fluid is well established in high-pressure chromatography and fluid extraction applications.