Predictions on the solubilities of substances in supercritical fluids have to rely on the equation of state. Consequently

it is very important to develop an equation of state applicable to supercritical fluids

especially for fluids approaching critical conditions. The p-V-T properties of 10 substances CO2

G2H4

C3H8

etc. in the supercritical region were calculated by the RK

RKS

PR

CS-RK and CS-vdW equations of gases state and the calculated results were compared with experimental data. It was found that all these equations of state were not adoptable to the supercritical region

especially at the points approaching critical. A modified RKS equation of state

employing molecular thermodynamics

was suggested: This equation of state was used to calculate the p-V-T properties in the supercritical region and was found to be of good accuracy. In the region approaching the critical point

deviations in calculations by this modified RKS equation were much smaller than those of other equations of state.