This paper reports the pressure-temperature conditions for the vapor + liquid + liquid + hydrate four-phase equilibrium in the systems of methylfluoride and water plus each of the following substances: cyclopentane, fluorocyclopentane, cyclopentene, and tetrahydropyran. The pressure ranges of the present measurements in the four systems are (0.138 to 2.998) MPa at temperatures from (287.9 to 305.9) K in the cyclopentane system, (0.122 to 2.560) MPa at temperatures from (290.1 to 307.0) K in the fluorocyclopentane system, (0.106 to 1.928 MPa) at temperatures from (283.6 to 300.8) K in the cyclopentene system, and (0.116 to 1.877) MPa at temperatures from (284.4 to 301.0) K in the tetrahydropyran system. These equilibrium pressures are lower by at least 0.6 MPa than those in the binary methylfluoride + water system, suggesting the formation of double hydrates with methylfluoride plus cyclopentane, fluorocyclopentane, cyclopentene, or tetrahydropyran. The crystallographic structure of the hydrates is identified to be structure II based on the powder X-ray diffraction measurements.