The presence of molecular oxygen in the test environment (oxic conditions) induces up to a 200 percent increase in the adsorptive capacity of granular activated carbon for o-cresol compared with the capacity that was attainable under anoxic conditions. This phenomenon is attributed to the polymerization of adsorbate on the carbon surface in the presence of molecular oxygen. Molecular oxygen exerts little influence on adsorption kinetics during the first 10 h of adsorbate-adsorbent contact. Breakthrough curves are well predicted by independently determined adsorption equilibria and kinetic data collected under anoxic conditions. Includes 29 references, tables, figures.