Multi-component, multi-phase equilibrium analysis was used, to determine when a corrosion attack may occur and when an alloy may be resistant to corrosion at elevated temperatures. Although chemical equilibrium analysis does not consider processes governed by mass transport (diffusion) or other kinetic constraints, it provides a useful way to study the potential for corrosion in different gas environments. Comparison of chemical equilibrium calculations with the results of SEM investigations shows that equilibrium calculations usefully characterize the corrosion resistance of metals and alloys. Some examples are given and, in the case of AISI 310 and Alloy 613 in gasification environment, the agreement with practical experience is good. For corrosion in Diesel engines, calculations indicate that some risk for carburization or metal dusting exists with the alloy 13CrMo44. For the alloy Nimonic 80A, calculations indicate the presence of chromium oxides and aluminium oxides, and thus reduced corrosion risk.