In recent years, the technology of separating gas mixtures by forming hydrate has received increasing recognition, particularly the separation of light-gas mixtures. We performed an experimental and modeling study of systems containing hydrogen, methane, ethane and ethylene, both with and without the thermodynamic promoter tetrahydrofuran (THF) in water. Vapor-hydrate equilibrium data (P-T-x-y data) were measured for (H-2 + CH4), (H-2 + N-2 + CH4) and (CH4 + C2H4) gas mixtures in the absence and presence of THF. A relatively simple algorithm was used to calculate vapor-hydrate two-phase equilibria. The Patel-Teja equation of state, coupled with a van der Waals-Platteeuw-type hydrate model, was applied to calculate the equilibrium flash of vapor-hydrate phases. The parameters in the hydrate model were determined by correlating the experimental data of hydrate formation conditions. In addition, we predicted the composition of gas mixture in the hydrate phase when structure I and structure II hydrates coexisted in a (CH4 + C2H6) gas mixture. The test results indicated that proposed algorithm is adequate for predicting vapor-hydrate equilibria. Accurate predictions of single-stage equilibrium between the vapor and the hydrate phases are important for developing separation technology via hydrate formation. (c) 2008 Elsevier B.V. All rights reserved.