Department of Chemistry, Panjab University, Chandigarh-160014 Manuscript received 6 March 1974; accepted 23 September 1974 Chemisorption of oxygen on Graphon, a highly graphitised carbon black, on treatment with oxygen (400°), ozone (in water and carbon tetrachloride at ordinary temperature), hot conceu­trated nitric acid and oxidising solutions of ceric sulphate, potassium persulphate and hydrogen peroxide are reported. The surface covered by the oxygen, on various treatments, varies between 2.5 and 13.8 m2/g., before pre-activation and between 6.3 and 21.9 m2/g., after pre-activation of Graphon to 17.2 per cent burn-off. The B.E.T. (nitrogen) surface area of Graphon increases from 76 m2 to 98 m2/g., on activation; the maximum surface coverage by oxygen, therefore, corres­ponds to about 18 per cent before and 22 per cent after the burn-off. The chemisorbed oxygen comes off largely as carbon dioxide and to a much smaller extent as carbon monoxide. The pre­sence of oxygen imparts acidity to the surface which, however, is not equivalent to the amount of CO2-complex formed. The presence of oxygen imparts hydrophilicity to the surface although it does not alter benzophilicity of the surface to any noticeable extent.