Following the report from the National Research Council of Canada in 1987 on a new hydrate structure, Sloan and co-workers reported the first structure H hydrate phase equilibrium data in 1992. The present work also reports structure H hydrate data for the methane-2-methylbutane-water, methane-2,2-dimethylbutane-water, methane-tert butyl methyl ether-water and methane-adamantane-water systems. In addition, data in the presence of NaCl were obtained for the first three systems and are reported for the first time. The data indicated that the structure H hydrate formation pressure, at a given temperature, is lower than the methane hydrate (structure I) formation pressure and that the presence of the salt caused a substantial inhibiting effect.