An electrolyte EOS based on Peneloux's non-electrolyte PR-EOS has been applied to the prediction of the temperature associated to the formation of gas hydrate from water-methanol-salts solutions. Original assumptions have been developed to allow the calculation of model ionic parameters from experimental solvation diameters. A mixing rule is used for the extension of the approach to water-methanol mixed solvents solutions. When applied to systems with CH4 and CO2 hydrates, the deviations between predicted equilibrium temperatures and calculated ones is less than I K over a wide range of conditions.