The determination of conditions at which clathrate hydrates are thermodynamically stable is important in applications such as offshore gas exploitation and energy storage. Adsorbed gas molecules occupy different cavity types within the hydrate lattice and this plays a significant role in the thermodynamic stability of clathrate hydrates. The occupancy of cavities in the hydrate lattice can be studied by undertaking Grand Canonical Monte Carlo simulations. Such simulations were performed in this study for methane clathrate hydrate with several force fields. Langmuir-type adsorption isotherms were fitted to the results of the simulations. The use of a single type of adsorption site was validated for methane clathrate hydrate. The adsorption isotherms which were fitted to the results of the simulations were used to compute the clathrate hydrate phase equilibria, which compared favourably with results from the literature.