In this work, the modified Ergun equation was proposed to determine the sphericity of irregularly shaped oil shale particle groups. The experimental packed beds were constructed by using twelve different oil shale particle groups, one sinter particle group and one pellet particle group to validate the applicability of this method. The effect of bed length, particle size and superficial velocity on pressure drops was studied. The equivalent volume diameters of the particle groups were determined and compared in different ways, and the relation between sphericity and equivalent volume diameter of Jimsar oil shale particle groups was obtained. The current experimental investigation shows that the modified Ergun equation is reliable to be used to determine the sphericity of irregularly shaped oil shale particle groups, and the geometric average works well to represent the equivalent volume diameter of sieved oil shale particle group. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B. V. and The Society of Powder Technology Japan. All rights reserved.