Treatments of 1000°-outgassed sugar charcoal with increasing amounts of nitric acid as well as with aqueous solution of chlorine, potassium persulphate and hydrogen peroxide result in chemisorption of increasing amounts of oxygen giving rise mostly to CO2-complex and in the case of the first two treatments also to concomitant increase in surface area and gasification of carbon. The complex formed initially is largely non-acidic, formed by the chemisorption of oxygen at unsaturated sites, but in later stages it is acidic formed by the association of two atoms of oxygen per active surface carbon atom. The continued treatment also causes conversion of non-acidic into acidic complex as well as disappearance of unsaturated sites and gasification of carbon. A suitable mechanism for these phenomena has been suggested.