Isothermal phase equilibrium (pressure-composition in the gas phase) for the ternary system of H-2 + CO2 + H2O has been investigated in the presence of gas hydrate phase. Three-phase equilibrium pressure increases with the H-2 composition of gas phase. The Raman spectra suggest that H-2 is not enclathrated in the hydrate-cages and behaves only like the diluent gas toward the formation of CO2 hydrate. This fact is also supported by the thermodynamic analysis using Soave-Redlich-Kwong equation of state. (c) 2005 Elsevier B.V. All rights reserved.