Photoinduced elimination of oxygen at a Ag(110)-p(2 x 1)-O surface has been studied by X-ray photoelectron spectroscopy, Auger electron spectroscopy, low energy electron diffraction, photodesorption mass spectrometry, and temperature-programmed desorption. Upon UV photoirradiation (lambda less than or equal to 400 nm) at room temperature the coverage of oxygen decreases and the structure of Ag-O chains changes from p(2 x 1) to p(4 x 1) only if the surface contains carbidic carbon. In contrast, the photoelimination of oxygen does not take place effectively if the surface is carbon free or contains graphitic carbon. The wavelength dependence of the reaction cross section suggests that substrate -mediated excitation is responsible for the photochemistry. Oxygen atoms are eliminated in the form of CO2 by the photoirradiation, indicating that an activated oxygen atom in the Ag-O chain reacts with a carbidic carbon atom at the surface to form CO that is further oxidized to CO2. As a side effect of the photochemistry, some carbidic carbon is converted to graphitic carbon. This could be due to the massive restructuring of the surface associated with the photoelimination of oxygen.