This paper presents phase-equilibrium pressure-temperature data for the clathrate hydrates formed in the three component systems each consisting of a hydrate-forming gas, a water-soluble freezing-point depression material, and water. These systems are {fluoromethane (CH3F) + propan-2-ol + water}, (fluoromethane + 2-methyl-2-propanol + water), and (fluoromethane + 2-propanone + water). The mole ratio of water and the water-soluble material (papan-2-ol, 2-methyl-2-propanol, or 2-propanone) was 17:1. The temperature range over which the phase-equilibrium measurements were performed extended to 267.6 K on the lower side and 295.8 K on the higher side. The phase-equilibrium pressures in these three systems were found to be lower than that in the binary (fluoromethane + water) system at a given system temperature. The crystallographic structure of the hydrates formed in the systems with 2-methyl-2-propanol and 2-propanone was determined to be structure II based on the powder X-ray diffraction measurements. (C) 2011 Elsevier Ltd. All rights reserved.