Our hypothesis is that the optimal storage pressure for the adsorbed xenon storage system is lower than that of the bulk xenon storage system, thereby allowing for thinner-walled and thus lighter pressure vessels in the adsorbed storage system. The important question our model addresses is whether the reduced mass of the pressure vessel in the adsorbed xenon system compensates for the (added) mass of the adsorbent required to store the xenon at a lower pressure. The answer to this question depends on the xenon adsorption isotherm in and density of the nanoporous material. We assess several nanoporous materials for xenon propellant storage, using experimentally reported xenon adsorption isotherms as input to our model. We find that MOF-505 and Ni-MOF-74 outperform the traditional adsorbent, activated carbon. However, when comparing the adsorbed and bulk xenon storage systems, we find that none of the nanoporous materials considered compete with the bulk storage system in terms of reducing the overall mass of the storage system. On the basis of a strong relationship between the adsorbent performance and its xenon adsorption properties, our model suggests that an adsorbent must exhibit a saturation loading of xenon that exceeds ca. 94 mmol Xe/g adsorbent to outcompete a bulk storage system. We also find that nanoporous materials that exhibit high gravimetric surface areas tend to perform well for adsorbed xenon storage. Our conclusions rest on several simplifying assumptions, which we clearly list and discuss.