The super-high-rate anaerobic bioreactor (SAB) possesses outstanding potential to treat concentrated wastewater. The flow patterns of SAB were investigated through tracer pulse stimulus-response technique and cold-model tests. The flow patterns were demonstrated to be analogous to plug flow at low loading rate and to completely mixed flow at super-high loading rate. Mean dead spaces of SAB caused by biomass and hydraulic behavior were 6.98 % and 21.01 %, respectively. The relationship among the hydraulic dead spaces (V(h)), the volumetric hydraulic loading rate (L) and the volumetric biogas production rate (G) was represented by: V(h) = 0.7603 L + 0.1627 G - 4.0620. The V(h) was greatly influenced by G over L value. The volumetric efficiency could further be improved when SAB was operated at super-high loading rate. The volume ratio of V(N) and V(1) decreased as N increased and the optimum N was 3.00 or so. (C) 2010 Elsevier Ltd. All rights reserved.