Hydrothermal gasification of three different industrial waste streams (distillery, oil refinery and petrochemical complex) was investigated in a batch reactor. Catalytic activity of three transition metal oxide catalysts (MnO2, CuO and Co3O4) with various catalyst loadings (20, 40 and 60 wt%) was also studied at various temperatures (300-375 degrees C) and reaction times (15, 30, 45 min). It was revealed that distillery wastewater possessed a great potential for hydrogen production compared to other wastewaters. MnO2 was determined as a weak catalyst for hydrothermal gasification, while Co3O4 was the best choice according to both aspects of gasification efficiency and H-2 mole fraction. The order of catalytic activity of catalysts for hydrogen production was as follow: Co3O4 > CuO > MnO2. It was also observed that 40 wt% loading of Co3O4 was the optimum value to gain the maximum attainable hydrogen from distillery wastewater. Moreover, higher temperature (375 degrees C) and longer reaction time (45 min) were favorable for hydrogen production. Finally, it was concluded that catalyst effectiveness was much pronounced at lower temperature and longer reaction time. Char formation was also significantly inhibited by the addition of catalyst. (C) 2016 Elsevier B.V. All rights reserved.