Methanol synthesis has been studied in fixed beds of unpromoted Raney copper, zinc oxide promoted Raney copper and a commercial low pressure Cu-ZnO-Al2O3 methanol synthesis catalyst at 523 K and 4.5 MPa using synthesis gas containing various CO2/CO ratios, while keeping the H-2/(CO2 + CO) ratio constant. All catalysts produced similar patterns of carbon dioxide and carbon monoxide conversions with increasing space velocities. carbon monoxide conversions were initially low, for synthesis gas containing CO2/CO ratios less than one and did not achieve maximum values until the conversion of carbon dioxide had reached a constant level (approaching thermodynamic equilibrium for the zinc oxide promoted catalysts). For synthesis gas containing CO2/CO ratios higher than one, carbon monoxide conversions were depressed by carbon dioxide hydrogenation. The results suggest that ZnO is an essential component for higher methanol activities. Hydrogenation of carbon dioxide and carbon monoxide takes place on the copper surface and the carbon monoxide hydrogenation appears to require activation resulting from carbon dioxide hydrogenation.