A novel method is presented to study magnesium metal vapor condensation/oxidation in CO and CO₂ atmosphere at reduced pressures. Mg(s) was evaporated and mixed with an equimolar amount of CO or CO₂ at 1000 °C after which the gaseous mixture flowed through an air cooled tubular condenser. Measurements of the axial temperature profile, calculation of partial pressures and analysis of deposits within the condenser allowed for identification of deposition/condensation onset temperatures, supersaturation ratio and reaction mechanism. In the presence of CO₂, rapid oxidation of Mg(g) has been observed. In the presence of CO, no Mg(g) oxidation was found above 950 °C. Mg(g) oxidation observed at lower temperatures is believed to be initiated by CO disproportionation. The proposed mechanism is able to explain the increase in Mg metal yield with decreasing CO partial pressure. At a CO partial pressure <3 mbar, high Mg metal mass yields of >90 w% were found. The presented method is applicable to the study of a variety of metal vapor/oxidizer combinations e.g. of interest in metal and solar fuel production.