Theoretical potential profiles for Ar, Kr, and Xe occluded in an idealized 5A zeolite are calculated and used to evaluate the Henry's law equilibrium constants for these species. Calculations were made using the three common formulae to estimate the dispersion constants (Kirkwood–Mueller, Slater–Kirkwood, and London) and the theoretical Henry constants are compared with the values obtained directly from experimental equilibrium isotherms. For both Kr and Xe the Slater–Kirkwood formula gives the best agreement with the experimental values while, for argon, the London formula is best. At higher concentrations the isotherms for Kr can be well represented by a simple Langmuir expression with eleven sites per cavity while for Xe there appears to be a transition from localized sorption at low temperatures to a mobile adsorbed phase at higher temperatures. These conclusions are qualitatively consistent with the results of the theoretical potential calculations.