[en] The initial oxidation of molybdenum at high temperature (1600 to 900⁰C) under low oxygen pressure (3 x 10^-7 Torr and 8 x 10^-6 Torr) was investigated by means of a high resolution Auger-photoelectron spectrometer. The amount of oxygen in the surface could be measured both by Auger electron and photoelectron spectroscopy. Auger electron as well as photoelectron spectra could be measured at elevated temperatures. By these methods two types of oxygen could be distinguished in the initial stage of oxidation. In the high temperature and lower oxygen pressure region, oxygen is dissociatively adsorbed on the surface and when the temperature is lowered the amount of adsorbed oxygen increases gradually. The oxygen induced peak in the He I photoelectron spectrum changes its position and shape at about 1300⁰C under an oxygen pressure of 8 x 10^-6 Torr and, at the same point, the shape of the Auger peak for oxygen also changes. At this point the incorporated oxygen apparently begins to form Mo0₂. The molybdenum oxidation state is assigned by means of X-ray photoelectron spectroscopy. (author)