A volumetric equation of state for chlorotrifluoromethane (R13) and trifluoromethane (R23), developed an the basis of the most recent experimental data reported in the literature, is proposed. The auxiliary equations of vapor pressure and constant pressure specific heat capacity, which have been used to calculate the derived thermodynamic properties, are also given here. The equation of state formulated affords a very accurate description of the thermodynamic behavior of Rl3 and R23 over a wide range of temperatures and pressures both in the gas and liquid phases.