The photoelectrochemical characteristics of highly transparent nanoporoys WO3 films are described. The photocurrent versus excitation wavelength spectra of these photoelectrodes exhibit a maximum close to 400 nm and a significant photoresponse to the blue part of the visible spectrum. The observed conversion efficiencies attain 75% for the photogeneration of oxygen from 1 M aq HClO4 and reach 190% in the presence of methanol in the solution, denoting in the latter case the occurrence of a perfect photocurrent doubling. Experiments conducted under simulated solar AM 1.5 illumination resulted in steady-state anodic photocurrents of the order of several mA/cm(2).