This Letter deals with spontaneous oxidizing of CVD diamonds exposed to room-temperature atmospheric air that is studied thanks to electrical measurements in a 2-point flat contact probe. Obtained results are explained in terms of the dipole model, which actually predicts accumulation of electrons in the oxidized films and hence should claim for its n-type conductivity. Unfortunately, the surface resistance is found to slightly increase under oxidizing. Generally, obtained data give evidence of usefulness of simple electrical measurements in studies of sorption-related processes in solids. (C) 2004 Elsevier B.V. All rights reserved.