The phase and volumetric measurements of perfluoromethylcyclohexane + methane and perfluoromethylcyclohexane + n-decane and their ternary mixtures at 373.15 K and over a wide range of concentration are presented. The ternary mixtures are used to carry out a constant composition expansion test at 373.15 K. Measurements are made on the liquid bubble point and retrograde dew point pressures and on the single-phase density of the binary mixtures. A high-pressure high-temperature oscillating tube densitometer is used to measure the density.