In this paper, we present a simple thermodynamic model to describe phase behavior of gas hydrates with CH4, C2H6, C3H8, N-2, CO2 and their mixtures as guests. The model is based on equality of water fugacity in the liquid water and hydrate phases. The van der Waals and Platteeuw model is applied for calculating the fugacity of water in the hydrate phase. The Stryjek and Vera modification of Peng-Robinson (PRSV2) equation of state is used to evaluate the fugacity of water in the vapor and liquid phases. Binary interaction parameters are adjusted as a linear function of temperature. The Vapor-Liquid-Equilibria for the pure gas hydrates former have been predicted within 2.87% absolute average relative deviation and for the gas mixtures have been predicted within 3.43% absolute average deviation. The pure gas hydrate formation conditions have been predicted within 2.27% absolute average deviation. The hydrate formation conditions of gas mixtures have been predicted within AAD 3.72%. The results are in good agreement, demonstrating the reliability of the thermodynamic approach used in this work. (c) 2012 Elsevier B.V. All rights reserved.