Co-57-Mossbauer emission spectroscopy (MES) has been used to study the oxidation of cobalt as a deactivation mechanism of high loading cobalt based Fischer-Tropsch catalysts for the gas-to-liquids process. It was reported previously [Catal. Today 58 (2000) 32 1; Proceedings of the International Symposium on the Industrial Applications of the Mossbauer Effect, 13-18 August, 2000, Virginia Beach, VA] that oxidation was observed at atmospheric pressure under conditions that were in contradiction with the bulk cobalt phase thermodynamics. A high-pressure MES cell was designed and constructed, which created the opportunity to study the oxidation of cobalt based Fischer-Tropsch catalysts under realistic synthesis conditions. The cobalt catalyst preparation procedure was investigated by means of Fe-57-Mossbauer absorption spectroscopy, applying Fe-57 as a probe atom. Initial results indicate, although not yet conclusive, that a Co-57-MES catalyst can be prepared from the industrial prepared standard Co catalyst by an additional simple incipient wetness impregnation procedure.