Liquid-liquid dispersions which are occurring in the petrochemical and chemical industry are commonly separated in gravity settlers. To improve the settler design, phase separation of the dispersions was studied. The parameters having the greatest effect on the phase separation under gravity are drop size, drop-size distribution, as well as driving-force parameters for sedimentation and coalescence, namely density difference, viscosity and interfacial tension. The effect of the driving-force parameters on coalescence and sedimentation was characterized experimentally using a standardized batch-settling cell. The viscosity of the aqueous phase was increased by adding polyethylene glycol. This not only changed the viscosity but also the interfacial tension, having a significant impact on drop size. In high-viscosity systems the settling speed of swarm droplets will significantly slow down and droplet size will be smaller. Furthermore, internals in gravity settlers also have significant impact on the phase separation. The influence of internals was studied for inclined plates. It can be seen from the experiments that internals speed up coalescence for different viscosities and volume ratios between the phases up to a factor of two.