Four-phase equilibrium relations (gas + water + methylcyclohexanol + gas hydrate phases) have been measured in methane + methylcyclohexanol + water systems. We have discovered five new guest species of the methane structure-H hydrate: 1-methylcyclohexanol; cis-2-methylcyclohexanol; trans-2-methylcyclohexanol; cis-4-methylcyclohexanol; trans-4-methylcyclohexanol. Decomposition pressures of these methane-structure-H hydrates increase in this order under isothermal conditions.