Co-gasification of waste material with coal is a potentially effective method to utilize industrial wastes for power/heat and/or syngas generation and to solve their disposal problems. Canada with its large-scale oil sand industry is a major producer of unconventional oil. Petroleum coke is one of the main waste streams from oil sand refining processes. This study is an investigation of the effects of feed ratio, equivalence ratio and average particle size on the syngas production by means of co-gasification of petroleum coke with lignite coal in a stainless steel pilot scale fluidized bed gasifier with an inside diameter of 7 cm at 800 degrees C. Central composite design methodology was used for designing the experiments. Runs for 20 wt.% of petroleum coke in the feed at different equivalence ratios and particle sizes showed positive synergetic effects for syngas yield (up to 61.0 mol/kg of feed), H-2 + CO yield (up to 332 mol/kg of feed), carbon efficiency (up to 70.2%), and lower heating value (up to 9020 kJ/m(3)). Increasing the equivalence ratio improved gasification performance, but gas heating value and H-2/CO decreased. The effect of particle size (70-500 mu m) was insignificant. The use of petroleum coke (20 wt.% in the feed) has resulted in an improvement in the lignite coal gasification performance and can be considered as an effective utilization method for petroleum coke. (C) 2015 Elsevier B.V. All rights reserved.