Four-phase (ice + structure-H hydrate + large-molecule guest substance liquid + methane-rich vapor) equilibrium pressure-temperature conditions were measured at temperatures from 252 K to 272 K in systems of water + methane + LMGS, where LMGS is a large-molecule guest substance for a structure-H hydrate. The tested LMGSs were 2,2-dimethylbutane (neohexane), methylcyclohexane, and tert-butyl methyl ether. The results obtained in the 2,2-dimethylbutane system agree with the corresponding data reported by Makogon et al., which were the only data set on the structure-H hydrate phase equilibrium at temperatures below the freezing point of water. Among the three systems studied, the lowest equilibrium pressure at a given temperature was observed in the 2,2-dimethylbutane system, and the highest, in the tert-butyl methyl ether system.