A series of 20 commercial titanium dioxide samples, including Evonik P-25, Millenium, Huntsman, Crenox, Kronnos or Hombikat, have been tested as photocatalysts for hydrogen generation from water or water/methanol mixtures under monochromatic visible light (532 nm) or polychromatic simulated sun light irradiation. Remarkable variations in the photocatalytic activity were found from one sample to other. While the most active sample under monochromatic 532 nm irradiation was Millenium Tiona 595 and the photocatalytic activity ranking follows the order of the red shift of the absorption band onset, the ranking under simulated sun light was different and difficult to rationalize. Under simulated sun light irradiation, the most active samples were Evonik P25 and Dupont Ti-pure. Overall, our study is of interest to illustrate the large variation in the photocatalytic activities for commercial TiO2 samples depending on the photocatalytic reaction and conditions used. (C) 2013 Elsevier B.V. All rights reserved.