The amounts of tetrafluoromethane (CF 4 ) and hexafluoroethane (C 2 F 6 ) adsorbed on various adsorbents such as zeolite, activated carbon, and silica gel were measured experimentally using the volumetric method at 303 K in the pressure range from 3 kPa to 210 kPa. Experimental data for zeolite 13X, zeolite 5A, and activated carbon 20 to 40 mesh were obtained at 323 K and 343 K. Langmuir, Sips, and Toth isotherms were used to fit the experimental data. The isotherm parameters were determined, and the isosteric heats of adsorption were evaluated. Of the three isotherms tested, the Sips isotherm gave the most satisfactory fit of the experimental data. Zeolite 13X was the most favorable adsorbent showing large amounts of adsorbed CF 4 and C 2 F 6 .