The conversion of mineral magnesite to magnesium oxide, methane, carbon dioxide, and carbon monoxide in a hydrogen atmosphere at ambient pressure and overpressure without catalysts is discussed. Low temperature and elevated pressure facilitate CH4 formation whereas moderate to high temperature and low pressure facilitate CO formation. Methane is formed directly without any additional catalyst. CO2 emissions are decreased substantially in reductive calcination. Additional experiments revealed that reductively calcined magnesium oxide is a highly active reverse water-gas shift catalyst. CO formation from gaseous CO2 and H-2 at catalytically active magnesium oxide was reproducibly confirmed. Further reduction of carbon monoxide to methane is not catalyzed by reductively calcined magnesium oxide.