Attempts were made in this study to accurately correlate mutual solubilities of the CH4-H2O and the CO2-CH4-H2O systems with a conventional two-phase flash method using cubic equation of state. A new set of model parameters for the CH4-H2O binary pair were presented for our previous published PRSV + WS (NRTL) model to enable flash calculation and stability analysis for the CH4-H2O and the CO2-CH4-H2O systems over the temperature and pressure ranges of 274-573 K and 0.1-150 MPa. The temperature corresponding to the minimum methane solubility in the aqueous phase is found around 345 K and this temperature is almost no change when pressure changes from 20 to 140 MPa for the CH4-H2O system. This observation is supported by both modeling results and experimental data. The model performance for the CH4-H2O and CO2-CH4-H2O systems was validated by a large amount of experimental data available to us and two previous published models (DM2006 and SW1992). As for the CH4-H2O system, the average absolute deviation of model calculated phase composition from the experimental data is around 4% for the gas phase and 7% for the aqueous phase. The phase equilibrium of a ternary system (i.e. CO2-CH4-H2O) can be reasonably well predicted by use of interaction parameters per binary pair (CO2-CH4, CO2-H2O, and CH4-H2O). A web-based computational tool for the proposed model is also provided (Supplementary Information). (C) 2017 Elsevier B.V. All rights reserved.