Polycrystalline tungsten oxide films of 1–1.2μm thickness were prepared by reactive sputtering at elevated substrate temperature (270°C) and under different oxygen partial pressures in the range from 0.8 to 2.1mTorr. At the lowest partial pressure the films were substoichiometric, showed increased disorder, and exhibited photocurrents of 0.6mA/cm 2 at 1.8V vs SCE in 0.33M H 3 PO 4 . At partial pressures of 1.4mTorr and greater, stoichiometric WO 3 films were produced which exhibited photocurrents of 2.4mA/cm 2 at 1.8V vs SCE. It has been determined that the photoelectrochemical performance of slightly substoichiometric films is adversely affected by changes in optical properties, while the photocurrents of severely substoichiometric films suffer additionally from poor carrier collection.