Hydroformylation of cyclohexene was studied with a catalyst system of Ru-3(CO)(12) and LiCl using H-2 and CO2 instead of CO in NMP. The influence of H-2 and CO2 pressures on the total conversion and the product distribution was examined. It was shown that increasing total pressure of H-2 and CO2 promoted the reverse water gas shift reaction and increased the yield of cyclohexanecarboxaldehyde. Its hydrogenation to cyclohexanemethanol was promoted with increasing H-2 pressure but suppressed with increasing CO2 pressure. Cyclohexane was also formed along with those products and this direct hydrogenation was suppressed with increasing CO2 pressure. The roles of CO2 as a promoter as well as a reactant were further examined by phase behavior observations and high pressure FTIR measurements.