Photoemission spectroscopy (PES) has been used to study oxygen adsorption on the ZrC(111)surface between room temperature (RT) and 1000 degrees C. At RT oxygen is adsorbed dissociatively forming a (1x1)overlayer, which is accompanied by a monotonic increase in the work function (Delta phi = 1.0 eV at saturation). On the other hand, the work function decreases when the surface is reacted with oxygen at 1000 degrees C (Delta phi = -0.55 eV). PES studies were made on the adsorbed state of oxygen and it is proposed that the adsorbed oxygen atoms penetrate the surface and settle at a subsurface site at 1000 degrees C. (C) 1998 Elsevier Science Ltd. All rights reserved.