Inhibitors having relatively strong oxidizing anions, such as sodium chromate and nitrite, passivate iron both in the presence of air and in deaerated solutions. Much weaker oxidizing agents such as sodium tungstate and molybdate behave similarly to chromate and nitrite in the presence of air but do not prevent corrosion in deaerated solutions despite the fact that potential/time and polarization curves indicate that slow film formation is occurring. Tungstate ions, however, are effective oxidizing agents toward iron when discharged anodically at high current density.