Dark fermentative H(2) production (DFHP) has received increasing attention in recent years due to its high H(2) production rate (HPR) as well as the versatility of the substrates used in the process. For most studies in this field, batch reactors have been applied due to their simple operation and efficient control; however, continuous DFHP operation is necessary from economical and practical points of view. Continuous systems can be classified into two categories, suspended and immobilized bioreactors, according to the life forms of H(2) producing bacteria (HPB) used in the reactor. This paper reviews operational parameters for bioreactor design including pH, temperature, hydraulic retention time (HRT), and H(2) partial pressure. Also, in this review, various bioreactor configurations and performance parameters including H(2) yield (HY), HPR, and specific H(2) production rate (SHPR) are evaluated and presented. (C) 2011 Elsevier Ltd. All rights reserved.