AES and EELS are used to study Ihe effect of oxygen on the FeS, surface. The n u i n Auger Fe M,.,n' attenuates with increased oxygen exposures and shifts to Lower kinetic energy while the high kinetic energy feature due to an 'autoionization process' remains unaltered in energy. The EELS spectra measured as a function of oxygen exposure clearly indicate the formation of iron oxide similar to that of o-Fe20,. For the Fe& + O2 system, we shou, that U , is negligibly small and is in good agreement with the estimated Ucff for Fe203. A slight change in the S L3W Auger peak is observed on adsorption of oxygen and the formation of sulphur oxides is ruled out.