Carbon dioxide and hydrogen will react over iron at 800° to 1 000°K and 1 bar pressure yielding water, carbon monoxide, methane, and carbon. In addition, iron oxides and carbides form during reaction. Phase diagrams are used to analyze this complex reaction system. Data are presented which suggest that the formation of magnetite (Fe3O4) or wustite (FexO) inhibits carbon formation. The water yield thus observed is limited by the time dependent iron‐iron oxide‐gas equilibrium. Preliminary data also suggest that the formation of carbides has little effect on water yield.