High-rate cathodic photoelectrolysis of CO2 was conducted in a high pressure CO2 + methanol medium at p-InP electrodes. Current densities up to 100 mA cm(-2) were achieved, with current efficiencies up to 93% for CO production. The photoelectrochemical reduction of CO2 in the highly concentrated CO2-methanol solution was limited at the higher current densities (50-100 mA cm(-2)) by light intensity and not by the mass transport of CO2.