Isothermal phase equilibria (pressure-composition in the gas phase) for the quaternary system of H-2 + CO2 + tetrahydrofuran + water have been measured in the presence of gas hydrate phase. The lowest three-phase equilibrium pressure is obtained under the condition that the mole fraction of tetrahydrofuran in water is 0.056. The Raman spectroscopy results show that the H-2 and CO2 molecules competitively occupy the S-cage of structure-II (i.e., the H-2 molecule is enclathrated in the hydrate cages with a small amount of tetrahydrofuran at considerably low pressure).