The present work demonstrates the influence of experimental conditions such as weight ratio of sewage sludge to water (1/0-1/15), reaction temperature (200-350 degrees C), initial H-2 pressure (2.0-11.0 MPa), residence time (10-100 min) and type of catalysts (Na2CO3, Raney nickel, FeSO4, MoS2) on hydro-liquefaction process of sewage sludge. High amount of water improves the hydro-liquefaction process of sewage sludge by increasing the yield of bio-oil and the total conversion. The highest yield of bio-oil (47.79 wt.%) from sewage sludge was obtained with initial H2 pressure 5.0 MPa, reaction temperature 300 degrees C, and residence time 40 min. Under these experimental conditions, using weight ratio of sewage sludge to water 1/5, catalyst (FeSO4) - 5 wt.% of dry SS, mixing speed 350 rpm the obtained bio-oil had the highest energy recovery (69.84%), total conversion (70.64%) and its calorific value was 35.22 MJ/kg. (C) 2015 Elsevier Ltd. All rights reserved.