Reliable measurement of drop size distributions (DSD) in liquid–liquid dispersions are necessary for industrial process monitoring and control, as well as the in-depth study of emulsification mechanisms in order to develop accurate and phenomenological models to be used in population balance modelling. Two experimental devices were assessed: an in situ video probe coupled with an automated image analysis algorithm based on a circular Hough-transform and a focused beam reflectance measurement (FBRM). Their applicability was evaluated for o/w emulsions of silicone oil with mean droplet sizes between 50 and 200 µm. The in situ techniques have been compared to off-line laser diffraction, which was considered as the standard technique. The automated video treatment algorithm was improved to provide accurate detection rates for dispersed phase concentrations (by weight) ranging between 5% and 10–20% depending on the droplet sizes. The in situ nature of the video probe allows for a much finer temporal resolution during the early times of the emulsification, as well as giving more reliable measurements of not yet stabilised emulsions, when compared to off-line laser diffraction. The reconstructed DSDs from FBRM data consistently under-predicted the DSDs given by the other two methods, as it missed the largest droplets in the DSD. The influences of dispersed phase viscosity and concentration on the DSD, and the maximum and mean diameters have been evaluated. As the viscosity and concentration increased, the distributions move away from a classical uni-modal shape to more complex, multi-modal distributions due to more complex break-up phenomena.