Pressure and temperature conditions for the four-phase equilibrium in systems that include liquid water, structure H hydrate, methane gas, and liquid hydrocarbon substances (cycloheptane, cycloheptanone, or oxacycloheptane) were measured over the temperature range (273.5 to 284.1) K. The measurements indicate that, at 274 K, the equilibrium pressures of the systems with cycloheptane, cycloheptanone, and oxacycloheptane were lower by (1.6, 1.3, and 1.5) MPa, respectively, than those of the structure I methane hydrates in equilibrium with liquid water and methane vapor. Powder X-ray diffraction measurements of the formed hydrate samples confirmed structure H hydrates.