The equation of state (EOS) for aqueous electrolyte solutions developed by Furst and Renon (1993) has been extended to predict vapor-liquid equilibria (VLE) of ternary water-methanol-salt systems. The model parameters have been determined by fitting only binary data and related to the cationic Stokes diameters. The predictions of vapor-liquid equilibria of ternary water-methanol-salt systems are in good agreement with the experimental data. Then the extended EOS has been utilized to develop a predictive method for gas hydrate formation conditions in the presence of electrolytes and methanol. The new hydrate method employs the Barkan and Sheinin (1993) hydrate model for the description of the hydrate phase, the extended EOS for the vapor phase fugacity and for the activity of water in the aqueous phase. The agreement is good between the predicted hydrate formation pressures and experimental data.