The oxidation of ferritic stainless steels has been studied under solid oxide fuel cell (SOFC) interconnect "dual'' exposure conditions, i.e., simultaneous exposure to air on one side of the sample, and moist hydrogen as the fuel on the other side. The scales grown on the air side under these dual exposure SOFC conditions can be significantly different from scales grown on samples exposed to air on both sides. In contrast, no substantial difference was observed between scales grown on the fuel side of the dual atmosphere samples and scales grown on samples exposed to moist hydrogen on both sides. The anomalous oxidation of stainless steels at the air side depends on both alloy composition and thermal history. AISI430, with 17% Cr, suffered localized attack via formation of Fe2O3 hematite-rich nodules on the air side of dual exposure samples, while the spinel top layer of the air side scale of Crofer22 APU (23% Cr) was enriched in iron. For E-brite, with the highest Cr content (27%), no unusual phases were found in the scale on the air side, but the air side scale was less dense and appeared to be more prone to defects than the scale grown in air only. Increasing temperature and thermal cycling both accelerated the anomalous oxidation, which appeared to be related to the transport of hydrogen through the steel and its subsequent presence in the air side scale. (C) 2004 The Electrochemical Society.