Although some particle sizing devices have gained a lot of popularity, none of them is able to distinguish between drops and solids and few are able to handle viscous oily samples. This paper discusses the use of the optical microscopy, enhanced by the use of digital video capabilities and image analysis software, to characterize oil production wastes. Several thousands of particles were counted and their projected areas were measured. A discussion is given about the different corrections required in order to extract the most reliable information from the image analysis, overcoming some of the drawbacks of this kind of measurements. The technique developed here offers unique features like the determination of the fraction of droplets that exist in the form of non-coalesced agglomerates. When cross-linked with the results obtained by standard ASTM procedures, it allows to infer the amount of disperse phase that exists in the form of submicron droplets or large free water drops that are usually not sampled for microscope slides.