(111) textured Au films were oxidized under UHV conditions by exposing them to UV radiation and ozone. The Au films were characterized by x-ray photoelectron spectroscopy. The gold surface becomes heterogeneous upon oxidation : approximately 0.8 monolayer (ML) of the adsorbed oxygen is present as chemisorbed species. The rest of the adsorbed oxygen forms, on the average, a few ML thick gold oxide with a stoichiometry close to Au2O3. Both the oxide and the chemisorbed oxygen disappear slowly when heated to 150 degrees C. During isothermal decomposition at 200 degrees C, the oxide is transformed to chemisorbed oxygen prior to desorption. Both the chemisorbed oxygen and the gold oxide can be removed by rinsing with water. The surface is hydrophilic after the rinse. When contaminated gold films are exposed to UV/ozone, impurity oxides appear at higher binding energies than the binding energies of oxygen on clean gold samples. The impurity oxides are thermally much more stable than Au2O3.