Energies and configurations of the oxygen-atom adsorption on gold surfaces have been examined by using first-principles calculations. For the low coverage (<0.5), the adsorption energy, E-ad(O), for Au(111) is larger than that for Au(100), and the atomic adsorption on both the surfaces is stable against a free oxygen molecule. As the coverage increases, E-ad(O) ad decreases and E-ad(O) for Au(111) becomes smaller than that for Au(100), and finally the atomic adsorption on these surfaces becomes unstable against a free oxygen molecule. The dependence on the coverage and the surface orientation has been analyzed by the O-Au and O-O interactions in comparison with experiments. (C) 2010 Elsevier B. V. All rights reserved.