Iron and model alloys containing 2.25, 9, and 20 wt% Cr, 2, 4 and 6 wt% Al, 1, 2 and 3 wt% Si, and dilute Fe-Si-Al ternaries were reacted in dry and wet Ar-CO2 gases at 800°C. External oxide scales grew on Fe according to fast, linear kinetics in dry CO2. Additions of H2O accelerated the reaction until steady-state parabolic kinetics were achieved. High Cr content alloys developed slow-growing chromium-rich oxide scales. Dry CO2 mixtures produced faster rates than wet gas mixtures. Lower Cr alloys developed thicker iron oxide scales, featuring cavities, cracks and poor adherence, and sustained internal oxidation. The presence of H2O led to even higher oxidation rates. Aluminium additions to iron of up to 4 wt% provided no protection, but instead caused internal oxidation. A level of 6 wt% significantly slowed oxidation by forming a continuous Al2O3 layer. Silicon additions had little effect, apart from promoting internal oxidation. However, simultaneous alloying with aluminium and silicon strongly depressed corrosion rates. The effectiveness of different alloy additions is discussed, along with the effects of water vapour and carbon activities, in the context of oxyfuel combustion technology.