Silver-exchanged Y zeolites provide examples of unusual adsorption and also of 129Xe n.m.r. chemical-shift behavior of the encaged xenon atoms. In the present contribution, we obtained isosteric heats of adsorption from temperature-dependent measurements of the adsorption isotherms of xenon in these zeolites. We further substantiated the previously suggested model that considers two different silver cation sites in the supercages of these zeolites. The distinctly higher isosteric heats of adsorption on Ag + sites (26.5 and 31 kJ mol −1) in comparison to the sodium form of zeolite Y at low xenon concentrations (18.5 kJ mol −1) substantiate the view that a silver cation-xenon bond of presumably the d π – d π overlap type is set up.