Previously, diagrammatic methods of presentation have been used to study the thermodynamics of metallic corrosion in fused chlorides, and the method has now been extended to metal‐winning reactions. Diagrams in which the equilibrium potential E (relative to the standard chlorine electrode) in the system is plotted against the activity of oxide ion in the chloride melt (expressed as its negative logarithm, pO2−) are presented for the metals Mg, Ni, Zr, and Ti in contact with one or more of the chlorides , , , and , at 800°C. As an example of the use of diagrams, it is shown how they can be applied to metal extraction processes involving chlorides. The main advance here is that the method offers an approach to the prediction of impurity levels and is applicable equally well to electrowinning from fused chlorides and to reduction of chlorides by base metals. Levels of impurity, particularly of oxygen, in the metal product are obtainable directly from the diagrams.