Photocurrents flowing at AISI 301 stainless steel electrodes, polarized anodically in sulfate solutions of various pH, were related to the nature of the surface oxides formed in these environments. The oxides were identified by surface Raman and IR spectroscopies. Correlations among pH, surface coverage with different types of oxides and photocurrent were recognized by mapping Raman spectroscopy, optical microscopy and image analysis. A high photoresponse is mainly related to high surface coverage with magnetite, formed at high pH. Exposure to low- pH solutions gives rise to preferential formation of hematite. Magnetite formed at high pH is irreversibly transformed into hematite if the oxide layer is subsequently exposed to a low- pH solution.