The reactivity of metallic and oxidized copper Surfaces in methanol oxidation was studied in the 10(-2) mbar range. Transitions between the metallic surface and the two copper oxides, Cu2O and CuO, are being followed by the color changes of the sample and by ellipsometric measurements. Compared with a metallic copper surface, a partially oxidized copper Surface has higher reactivity toward production of formaldehyde, whereas the deeply oxidized surface (CuO) shows a higher activity toward total oxidation to CO2. Oxidation and reduction of the Cu Surface are associated with a strong change in the degree of roughening and with spatial inhomogeneities, as demonstrated by photographic imaging and by ellipsometric microscopy. (c) 2005 Elsevier Inc. All rights reserved.