A preliminary study of the corrosion films of stainless steel SUS304 was carried out by X-ray photoemission spectroscopy for supercritical water having no oxidant or reactant. The corrosion films produced by the supercritical water at 450 degrees C and 50 MPa were compared with those by anodic polarization in H2SO4 aqueous solution. The chemical states in the films were determined by factor analysis of Fe, Cr, and Ni 2p X-ray photoelectron spectra. Factor analysis of the passivated SUS304 surface was successfully carried out using four reference spectra, Fe metal, Fe3O4, Fe2O3, and FeOOH, with careful treatment excluding wustite Fe1-xO phase from the standpoint of thermochemistry. In the surface treated by supercritical water, the ratio of iron and nickel increased even when compared to the bulk composition of SUS304 and the major component of nickel was attributed to NiFe2O4. In contrast, the content of chromium decreased remarkably. This was explained by effective removal of CrO42- and its protonated form, HCrO4-, which are predicted in the Pourbaix diagram prepared for chromium in supercritical water (450 degrees C and 50 MPa). (c) 2005 The Electrochemical Society.