An inventory of released volatiles on Mars has been derived based upon Viking measurements of atmospheric and surface chemical compositionand upon the inferred mineralogy of a ubiquitous regolithassumed to average 200m in depth. This model is consistent with the relative abundances of volatiles (except for S) on the Earth's surfacebut implies one‐fifteenth of the volatile release of Earth if starting materials were comparable. All constituents are accommodated as chemical components ofor absorbed phases onregolith materials — without the necessity of invoking unobservable deposits of carbonatesnitratesor permafrost ice.