The progressive reaction of ozone and oxygen mixtures with charcoal at 26ยฐC was studied to specified weight-gains and to different subsequent weight-losses when outgassed at various temperatures. Although each ozone-treated adsorbent gave evidence of continuous decomposition when introduced into a vacuum adsorption apparatus, stability was obtained when the sample was cooled to 77"4ยฐK. The degassing is associated with an inherent unstability of the ozone-product formed and not to desorbed gases. The products were characterized by very large decreases in the nitrogen adsorption at 77-4ยฐK. Two explanations are examined to account for the adsorption behavior. First, the etching reactions that prevailed during the formation of the original carbon adsorbent can continue and lead to pore structures of greater diameters (and accordingly lesser specific surface area) than the original charcoal. Second, a blockage of the micropore openings to nitrogen molecules can take place due to the chemisorption of oxygen at the critical openings of the porous carbon structure. A sequence of three reactions is suggested to explain both the weight changes upon ozone treatment and the unique behavior of the nitrogen adsorption isotherms determined at 77-4ยฐK.