Molten oxide electrolysis (MOE) is the electrolytic decomposition of a metal oxide, most preferably into liquid metal and oxygen gas. The successful deployment of MOE hinges upon the existence of an inert anode capable of sustained oxygen evolution. Herein we report the results of a program of materials design, selection, and testing of candidate anode materials and demonstrate the utility of iridium in this application. An electrolysis cell fitted with an iridium anode operating at 0.55 A cm(-2) produced liquid metal and oxygen gas by the decomposition of iron oxide dissolved in a solvent electrolyte of molten MgO-CaO-SiO2-Al2O3. The erosion rate of iridium was measured to be less than 8 mm y(-1). The stability of iridium is attributed to a mix of mechanisms including the electrochemical formation and simultaneous thermal decomposition of a surface film of iridium oxide. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3560477] All rights reserved.