Isotherms for the adsorption of nitrogen (77 K), carbon dioxide (195–247 K) and sulfur dioxide (254–293 K) on polyvinylidene chloride have been measured volumetrically. The B.E.T. cross‐sectional areas of 18 Å2 (CO2) and 24 Å2 (SO2) are comparable to liquid density values. The isosteric heat of adsorption of CO2 is constant for 0.2 < θ < 0.4 and is lower than the latent heat of condensation. For SO2, the two are practically identical up to the monolayer. Entropy calculations show ‘supermobility’ in the case of CO2.