The behavior of TiO2and SrTiO3photoanodes in cells for the photoelectrolysis of H2O has been investigated for high‐intensity 351 364‐nm excitation from an Ar ion laser. Intensities up to 380 W/cm2have been used. For TiO2a small amount of surface decomposition is found after irradiation at high intensity, whereas SrTiO3undergoes no detectable changes. Current‐voltage properties for both electrodes are essentially independent of light intensity up to the level of 380 W/cm2, and there is little if any change in quantum efficiency for electron flow. Photocurrent densities have been shown to exceed 5 A/cm2for O2evolution. Data show that the energy storage rate associated with the SrTiO3photoelectrolysis can exceed 30 W/cm2; this represents the highest demonstrated rate of sustained optical to chemical energy conversion.