Carbon　monoxide　is　an　important　intermediate　in　supercritical　water　oxidation　processes.　Carbon　monoxide　oxidation　in　supercritical　H2O/CO2　mixtures　was　investigated　using　reactive　molecular　dynamics　simulations.　The　results　show　that　CO　mainly　converts　into　CO2　through　the　reaction　CO　+　OH　→　HOCO　→　CO2　+　H.　The　intermediate　HOCO　can　also　react　with　OH　or　O2　to　form　CO2.　The　overall　activation　energies　of　CO　oxidation　in　the　supercritical　medium　range　from　125.3　±　4.0–159.4　±　3.6　kJ/mol,　which　are　roughly　consistent　with　the　experimental　results.　Supercritical　water　not　only　provides　reactive　free　radicals　for　CO　conversion　but　also　acts　as　a　third　body　to　induce　some　chemical　events.　The　high　concentration　of　CO2　inhibits　the　production　of　OH　but　highlights　the　oxidizing　action　of　O　and　HO2.　Oxygen　increases　the　amounts　of　OH　and　HO2　through　the　reaction　H2O　+　O2,　thereby　promoting　the　conversion　of　CO.　©　2022　Elsevier　B.V.