Photocatalytic CO2-to-CO reduction using [fac-Re(bpy)(CO)(3)P((OPr)-Pr-i)(3)](+) (bpy = 2, 2'-bipyridine) occurred with high efficiency in a high-pressure CO2 gas/organic solvent system. At a CO2 pressure of 1.36 MPa, the turnover number for CO formation was 3.8 times that in the conventional normal-pressure (0.10MPa) system. Application of high-pressure CO2 gas greatly increased the CO2 concentration in the solvent phase. The high CO2 concentration enhanced the reaction of one-electron-reduced catalytic species with CO2, and effectively prevented the deactivation of the catalyst. (C) 2002 Elsevier Science B.V. All rights reserved.