Four-phase (liquid water + hydrate + liquid hydrocarbon + vapor) equilibrium data are reported for structure II hydrates of methane + cyclohexane or cyclopentane and a ternary mixture gas (methane = 91.96 mol %, ethane = 5.13 mol %, propane = 2.91 mol %) + cyclohexane in the pressure range (0.165 to 9.486) MPa and the temperature range (273.83 to 301,90) K. The equilibrium pressures of the experimental systems of methane + cyclohexane or cyclopentane are concededly lower than that of the system of pure methane at a given temperature. The presence of cyclohexane inhibits hydrate formation, rather than promoting it, at higher temperatures in the test system of the ternary mixture gas + cyclohexane.