For both open and closed supercritical carbon dioxide (sCO2) cycles there is considerable interest in increasing the size and efficiency of such systems for power generation with efficiency increased by increasing the peak temperature above 700°C. As an initial assessment of potential Fe- and Ni-base structural alloys for this application the current project is screening a wide range of alloy coupons in 500h exposures at 200 bar high purity carbon dioxide from 400°-750°C. At the lower temperatures more Fe-base alloys were exposed while above 600°C more Ni-base alloys were exposed as the Fe-base alloys with <25%Cr formed thick Fe-rich oxides. For the more highly alloyed materials at 700° and 750°C the mass change after 500h in sCO2 was similar to that observed after exposure for 500h in 1bar carbon dioxide or laboratory air. Initial characterization has focused on light microscopy of polished cross-sections to measure the thickness of the reaction product but additional characterization is in progress. Research sponsored by the U.S.Department of Energy Office of Fossil Energy Coal and Power R&D (R. Dennis program manager).