Kellogg predominance area diagrams are normally used to present dominant solid species as a function of two gaseous species in the absence of liquid water. Originally applied to pyrometallurgical processes, such diagrams are also used to study geochemical reactions as well as ceramic and semiconductor processing. Two methods are commonly used for their construction. With the line method, predominant areas are drawn by bounding adjacent species using equilibrium constants. By comparison, the point method identifies the stable species that satisfies, not only the equilibria of the whole system, but also the mass input from each component. This method normally assumes each solid species to be independently separated, but all involving gases or liquids to be in one mixture of stable phase. For non-aqueous systems, it turns out that a free energy minimization algorithm operating under these constraints is most suitable. For multicomponent systems, these two methods can yield different diagrams due to the way how the components are treated. The line method starts from ligand component by determining the predominant areas from the member of its constituents. The species from the main component are then distributed in each isolated ligand species. The point method treats all components to be the same restricted only by the mass input. Numerical examples from commonly used processes are illustrated, including oxidation of Cu-Fe-S and Zn-Fe-S, chlorination of Ti-Fe-O, volatilization of Cu-Cl, and hot wire vapor deposition of polynuclear silicon from silane gas.