Improvement in diluted bitumen dewatering performance with improved mixing conditions was evaluated using a factorial design of experiments. The experiments were carried out in a confined impeller stirred tank (CIST), which provides quantifiable and repeatable mixing conditions with more uniform turbulence and flow than a conventional stirred tank. Four variables were considered: mixing time, energy dissipation, bulk concentration, and injection concentration of demulsifier active ingredient. Results showed that all four variables play an important role in demulsifier performance. As expected, demulsifier bulk concentration plays a decisive role. Lowering the injection concentration improved demulsifier performance. This indicates that strong mesomixing effects are present due to high local concentrations in the feed plume. Increasing energy dissipation and mixing time also substantially improved demulsifier performance, allowing the same water separation at a significantly lower demulsifier bulk concentration. Mixing time and energy dissipation were successfully combined into a single variable, mixing energy, which can be used to scale-up mixing conditions. (C) 2015 Elsevier B.V. All rights reserved.