In this study, the photosynthetic hydrogen production rates by some strains of green microalgae were investigated. Three strains of Chlorella isolated from and soil and foggaras's water in the Algerian Sahara were used. Chlorella sorokiniana strain Ce, Chlorella salina strain Mt and Chlorella sp strain Pt6 produced hydrogen gas under sulphur-deprived conditions, but its rate was dependent on strain type and oxygen partial pressure in medium. In C. sorokiniana strain Ce, the maximum value of hydrogen accumulated was 147 ml at 222 h at 2% of O(2) pressure. Compared to C. sorokiniana strain Ce, C. salina strain Mt and Chlorella sp strain Pt6 produced less amount of hydrogen, but they were able to sustain with an O(2) partial pressure of up to 11-15.4%. Our data were compared with hydrogen production by Chlamydomonas reinhardtii. In this communication, the relationship between physiological behaviour, biochemical characteristic (starch and protein) and rates gas production (O(2) and H(2)) was also specified. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.