Clathrate hydrate of methane became of importance as an energy resource and as a problem to natural gas industry. Data are available for various phase equilibria, but methane solubility in H-L-W equilibria was not reported. In this study, the methane solubility were measured in the pressure range from 2 to 20 MPa and in the temperature range of 273-285 K. Applicability of the lattice fluid equation of state by the present authors was also investigated for the unified description of various phase equilibria with Langmuir constants in the van der Waals and Platteeuw model for hydrates and hydrogen-bonding free energy of water fitted to data, the model was found to consistently describe various two- and three-phase equilibria of L-W-V-CH4, H-L-W-V-CH4, H-I-V-CH4, H-L-W and H-V-CH4. With a single binary interaction parameter, good agreements between observed and calculated results were obtained except for water contents in methane-rich phase of L-W-VCH4, equilibria where the error becomes larger.