An improved set of all the thermodynamic and molecular properties required for the prediction of the existing 20 systems of Structure H (sH) hydrate phase equilibrium data is presented The statistical thermodynamics model was based on the van der Waals and Platteeuw theory, and the spherical core Kihara potential was used for guest-water interactions. Optimized Kihara parameters and reference thermodynamic properties were derived fi om experimental data of over 20 sH hydrate forming systems. The model could fit all the existing sH hydrate data within an accuracy of +/-6%. Inhibitor predictions were also shown to fit recent data with no adjustable parameters. The feasibility of using hydrate cage occupancies to derive refined Kihara parameters of the guest molecules was investigated. Possible existence of sH hydrates at cryogenic temperatures was also established based on the model.