Based on the intermolecular potentials, Duan et al. (1992,1996) developed an equation of state (EOS) for supercritical fluids. This equation reproduces thousands of PVT data points for both pure systems and mixtures below 2. 0 GPa (20 kbar) from the supercritical temperature to about 2000 K. Furthermore, this EOS can predict all available experimental data (PVT properties, fugacity, enthalpy, and supercritical phase seperation) with accuracy close to experiments from 1. 3 times of the critical temperature and zero pressure up to about 2000 K and 10 GPa (100 kbar) for the fluids H2O, CO2, CH4 and N2 and their mixtures.