Twelve adsorption isotherms of oxygen on a high surface activated carbon have been collected with a volumetric apparatus for the range (118-313) K and (0-10) MPa. The isosteric enthalpy change of adsorption was evaluated on the basis of these isotherms. It shows a descending trend with the increased amount adsorbed. A model is presented for the experimental isotherms on the basis of the Gibbs definition and the determination of absolute adsorption. The model fits the isotherms well for the range of experiments. On the basis of the measurements, the enhancement effect of adsorption for the storage of oxygen was proven.