Three newly discovered H-2 producing bacteria namely Clostridium perfringens strain BC, Clostridium bifermentans strain WYM and Clostridium sp. strain Ade.TY originated from landfill leachate sludge have demonstrated highly efficient H-2 production. The maximum H-2 production attained from these isolates are in the descending order of strain C. perfringens strain JJC > C. bifermentans strain WYM > Clostridium sp. strain Ade.TY with yield of 4.68 +/- 0.12, 3.29 +/- 0.11, and 2.87 +/- 0.10 mol H-2/mol glucose, respectively. The result has broken the conventional theoretical yield of 4 mol H-2/mol glucose. These isolates were thermodynamically favourable with Gibbs free energy between -33 and -35 kJ/mol (under process conditions: pH 6, 37 degrees C and 5 g/I, glucose). All three isolates favour butyrate pathway for H-2 production with the ratio of acetate and butyrate of 0.77, 0.65 and 0.80 for strain JJCC, WYM and Ade.TY, respectively. This study reported provides a new insight on the potential of unique bacteria in H-2 production. (C) 2017, The Society for Biotechnology, Japan. All rights reserved.