Power cycles in the fossil energy, nuclear, and concentrated solar industries, using pure supercritical CO₂ (sCO₂) as the working fluid, have been proposed that offer significantly improved conversion efficiency and lower levelized cost of electricity over current power systems. High creep strength nickel-base alloys are proposed for use at the higher temperature portions of the power cycles. In this study a series of Ni-xCr model alloys (where x = 5, 12, 14, 16, 18, 20, 22, 24) were exposed to both sCO₂ at 700°C/200 bar for 1500 h and atmospheric pressure CO₂ at 700°C for over 5000 h. In both tests, all Ni-Cr alloys, even the low-chrome Ni5Cr alloy, maintained low oxidation rates and chromia scales. For CO₂+H₂O+O₂ mixtures at 750°C/1 bar, all alloys except Ni5Cr exhibited low oxidation rates and chromia scales. However, in other environments (air at 700°C/1 bar and steam at 700°C/200 bar) more Cr was needed to maintain low oxidation rates and chromia scales. This result shows that Ni-Cr alloys appear to be quite robust with respect to oxidation resistance in the pure and predominantly CO₂ environments found in sCO₂ power cycles.