Calorimetric measurements of the immersion enthalpy in different liquids of a set of regenerated activated carbons have been employed to analyze the effect of a regeneration process on the extension of the accessible Surface area and the hydrophobic character of the carbons by comparison with the original carbon, The modifications in the hydrophobicity of the activated carbons are quantified by the analysis of the surface free energy of the solids and its dispersion and non-dispersion components. It has been found that regeneration treatment of the original carbon increases its accessible surface area and hydrophobicity. However. the opposite effects take place when regeneration is done on the same carbon previously saturated with p-nitrophenol (PNP) or p-chlorophenol (PCIP). (C) 2002 Published by Elsevier Science B.V.