An activated carbon with developed porosity and surface area (S-BET = 2387 m(2) g(-2)) was prepared by chemical activation and then oxidized with ammonium peroxydisulfate. The oxidation treatment destroyed mesopore walls leading to a severe surface area reduction. Specific thermal treatments were carried out in different portions of the oxidized sample to selectively remove the oxygenated surface complexes. The combination of different techniques revealed that thermal treatment between 300 and 500 degrees C produces a strong reorganization of oxygenated groups on the chemical structure of carbons. CO2-evolving groups (around 75 wt.%) are selectively transformed into CO-evolving groups. These processes only occur inside the pores, and involve CO2 desorption and re-adsorption in this temperature range. At a higher treatment temperature (700 degrees C), re-oxidation is prevented and the surface chemistry becomes quite similar to the original activated carbon.