Cokes are used in several high temperature metallurgical processes as cheap reducing agents, for energetic aspects, and because of some of their physical properties, such as sufficient electrical conductivity, to serve as electrode material. Petroleum and metallurgical cokes contain impurities, like S, Fe, V, Na, etc. that can affect, as catalysts, the rate of desired or undesired chemical reactions. As impurity contents in cokes tend to increase, thermodynamic analysis of the high temperature behavior of impurities can help explaining the reactions in which they are involved. Recently the authors developed thermodynamic models both for organically bounded elemental impurities in carbon (S, H) and for inorganic components, such as salts, sulfides, oxides and carbides. In this presentation, the authors will show how the combine use of both types of thermodynamic models and computation of temperature/potential diagrams can help in explaining the role of such impurities.