The phase behavior of microemulsion systems consisting of oil, water and non-ionic surfactants can lead to emulsions with unique properties: by adjusting temperature and composition a system with three liquid phases is obtained. These systems can be used as solvent systems for reactions such as the hydroformylation of long-chained olefins. Knowledge of the occurring dispersion and coalescence processes is crucial for process optimization and control. Using an endoscope measurement technique in a stirred tank, relevant criteria that determine the formation of complex droplets by the two dispersed phases such as multiple emulsions are defined. The influence of the third phase on dispersion and coalescence is discussed by analyzing the drop sizes of the dispersed phases in agitated systems in situ. Furthermore, the impact of the third liquid phase on the slope of sedimentation and coalescence curves is analyzed in subsequent phase separation experiments. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.