It has been known for years that the performance of a demulsifier in diluted bitumen dewatering improves up to a certain demulsifier bulk concentration., After this limit, the water removal deteriorates: This phenomenon is called overdosing. In this paper, the effects of mixing-energy and demulsifier injection concentration on-water removal are studied in systems with a high bulk demulsifier concentration. The experiments were conducted in a confined impeller stirred tank (CIST), which provides well-controlled mixing conditions with more uniform turbulence and flow than a conventional stirred tank. The results show that an increase in mixing energy and pre-dilution of the demulsifier may be able to overcome overdosing effects at a high bulk (mean) concentration. If the mixing conditions are well-designed, high local demulsifier concentrations at the feed point are avoided and the demulsifier can perform well, even at high bulk concentrations. The best demulsifier performance in an overdosed system was obtained with a combination of high mixing energy and low injection concentration, where over 80% of the water content was separated at a demulsifier bulk concentration that showed severe overdosing behavior at poor mixing conditions.