<p>Most high-temperature alloys are protected by chromia scales formed on their surfaces during service. Water vapour negatively affects the performance of these scales, an effect this work seeks to overcome. Binary Fe-Cr alloys containing 10 or 20 wt.% Cr failed to produce chromia scales in Ar-H₂O(g) atmospheres at 750 °C, instead forming fast-growing iron-rich scales as the alloys were consumed. An alloy Cr concentration between 20 and 30 wt.% is required to form protective Cr₂O₃ under these conditions, whereas 10 wt.% Cr suffices in oxygen. To achieve the benefits of lower Cr levels, the effects of selected minor alloy additions were explored. Alloying with each of 1Ti, 2Mn, 1Si, and 0.1Ce (wt.%) was found to counteract the strongly negative effects of water vapour, leading to thin protective scale development. Characterisation of these scales allowed consideration of alloying and water vapour effects on diffusion processes supporting oxidation.</p>