Adsorption of xenon atoms in the α-cages of NaA zeolite has been studied using129Xe NMR spectroscopy to probe directly the distribution and configuration of molecules in confined, microporous environments. The129Xe NMR spectrum is sensitive to subtle changes in xenon environment, so relative populations of α-cages containing different numbers of xenon guests can be determined and the effects of other co-adsorbed species monitored. On the basis ofl29Xe NMR spectra, the distribution of xenon atoms among NaA α-cages is shown to exhibit a marked dependence on the pressure at which the xenon guests are introduced.129Xe NMR spectra recorded at 200 K reveal that xenon atoms in the NaA α-cages experience diminished mobility (resembling condensation phenomena) at higher temperatures than in the bulk gas of equivalent density. Thus, the chemical potential of adsorbed xenon can be investigated experimentally as a function of both temperature and guest density. The density dependence of thel29Xe chemical shift in Xe/NaA and in bulk xenon gas shows that Xe-Xe interactions in the proximity of the NaA cage wall are important in α-cages containing more than five xenon guests. This trend is linked to entropic effects which may enhance xenon adsorption in the confined environment of the NaA α-cages.