The DSC technique (Differential Scanning Calorimetry) was applied to the study of water-in-crude oil emulsions, which naturally form after an oil spill. The resulting emulsions contain between 50 and 80% seawater and they are often heavy materials, hard to recover mechanically, treat or burn. It is therefore important to assess their stability in order to optimize their treatments. A great variety of techniques are available for the assessment of emulsions stability. They are generally based on the analysis of the droplets size distribution. Unfortunately, most of the usual techniques can not be applied to opaque water-in-oil emulsions. The most useful method to characterize the stability of emulsions is of course the "bottle test". It consists in monitoring the extent of phase separation with time. This type of test provides a significant amount of information relating to both the stability of the emulsion phase and the clarity of the separated water, but it is very empirical. The DSC technique is generally used to determine the composition of water-in-oil emulsions. It is the only technique capable of distinguishing free water from emulsified water. It was shown in this study that it is a very useful technique, which allows the study of the evolution of the droplet size distribution as well as a precise determination of the water content.