The hot corrosion of alloys comprises a complex series of interacting processes. Despite the difficulties involved, the thermodynamic analysis of corrosion ought to take into account the multicomponent nature of the alloy, the constitution of the gas, and the microenvironments present in the corrosion layer. Most importantly the metallic, oxide, sulphide, and salt phases ought to be treated as solutions (mixtures). The methods for assessment and calculations involving solution phases are demonstrated by reference to the salt system NaCl-NaOH-Na2CrO4-Na2S04and its equilibrium with Cr2O3as the protect!ve oxide layer and the gaseous combustion products. The data requirements assa.ciated with these developments and their possible application to kinetic analysis are discussed.