Three-phase equilibrium conditions (aqueous liquid-vapor-hydrate) of four pure gases, five binary, five ternary mixtures and five natural gases were measured in the temperature range of 273.5-298 K and pressures of up to 25 MPa. The measurements were carried out in a high-pressure cell applying the isochoric method. The results obtained with the pure gases confirmed that the total measuring error of the apparatus is within 1%. The binary and ternary mixtures were measured as a basis for fitting the Kihara potential parameters in the calculation method suggested by van der Waals and Platteeuw. The results obtained with the natural gases show the expected dependence of gas composition on the equilibrium conditions. The results are in good agreement with the experimental data.