Oxygen is widely used at elevated partial pressures to facilitate decompression, yet the optimum dosage and the magnitude of the beneficial effects are poorly known. This is because oxygen enhancements, expressed as increases in the allowed pressure reductions, are small and easily masked by individual variation. Furthermore, oxygen can also produce detrimental results, and the range from a therapeutic to a toxic dose is narrow. Berhage and McCracken recently reported two massive investigations involving 1185 rats and 60 experimental conditions. These authors suggest that the conventional concept of an "equivalent air depth" (EAD) is untenable and that oxygen must be considered in calculating the totat tissue gas tension. We find instead that the observations of Berghage and McCracken are compatible with a model in which the tensions of oxygen and carbon dioxide dissolved in tissue are taken into account, and that this model, in turn, agrees with EAD predictions of oxygen enhancements for subtoxic oxygen pressures.