Fermentative hydrogen production has been carried out both in batch and continuous system using recombinant Escherichia coli BL 21. Effect of various process parameters, viz. size of inoculum, initial medium pH, initial substrate concentration, temperature and dilution rate, was examined with respect to maximum hydrogen productivity. Maximum hydrogen production rate obtained in this study was 66 mmol/(1 h) using glucose as substrate at a dilution rate of 0.55 h(-1) in the immobilized whole cell bioreactor. Black strap molasses, a by-product of sugar industry, was found suitable as a feedstock for fermentation using which maximum rate of hydrogen production was 97.4 mmol/(I h). Energy analysis reveals that the percentage of gaseous energy recovery obtained in this study using recombinant E. coli BL 21 and considering glucose as a substrate was 26.68%. A comparison of hydrogen production characteristics between the wild strain Enterobacter cloacae IIT-BT-08 and that of the recombinant E. coli BL 21 indicates that optimum initial pH, initial glucose concentration and reaction temperature are almost comparable and/or marginally same for both the strains. However, the yield of hydrogen (mol H-2/(mol glucose)) with the recombinant strain was 3.12 mol H-2/(mol glucose) which was much higher than that reported for the wild strain. (c) 2005 Elsevier Ltd. All rights reserved.