This paper presents the results of corrosion tests carried out on a series of Fe-12% Cr alloys in coal gasification environments at 600°C. The effects of both Si and Ti on corrosion resistance are assessed using data obtained from a commercial 12%Cr alloy, Type 410, three specially cast “model” 12%Cr alloys containing 2.7% Si and with Ti levels of 0%, 0.4% and 0.7%, respectively, and higher alloy heat exchanger materials, an 800-type, and an FeCrAl ODS alloy. Tests carried out in mixed sulfur-containing, low-pO2 gases under either thermodynamic equilibrium conditions (H2-based) or conditions where equilibrium was not established (CO-based) showed that Si has a strongly beneficial influence on corrosion resistance and that Ti can provide a small additional improvement. The kinetics of corrosion are presented in terms of weight-change and metal-loss measurements and the synergistic influences of Si and Ti are discussed and corrosion resistance compared with that exhibited by the higher alloy materials. Keywords: corrosion, non-equilibrium gas, heat exchanger alloys, alloying additions, development alloys