An 18-coefficient modified Benedict-Webb-Rubin equation of state of HFC-125 (pentafluoroethane) has been developed. Correlations of vapor pressure and saturated liquid density are also presented. This equation of state has been developed based on the reported experimental data of PVT properties, saturation properties, isochoric heat capacities, and speeds of sound by using a least squares fitting. This equation of state is effective in both the superheated gaseous phase and the compressed liquid phase at pressures up to 68 MPa, densities to 1700 kg m(-3), and temperatures from 170 to 475 K, respectively.