A method for characterizing and predicting the performance of emulsion breakers has been developed which involves the relationship between the preferred alkane carbon number (PACN) of the demulsifier to the equivalent alkane carbon number (EACN) of the crude oil and the salinity of the emulsified aqueous phase. This procedure can be used both to chose the proper emulsifier for field use and to develop effective new compounds by determining the effect of changes in molecular architecture and interfacial properties on performance. Parameters which have been studied include chemical type, molecular weight, degree of branching, partition coefficient between the water and oil phases, interfacial tension reduction and interfacial viscosity changes. The importance of each of these properties to performance will be discussed. Introduction The design and application of oilfield demulsifier compounds has historically involved the evaluation of numerous products and the bottle testing of even more numerous blends in order to arrive at a product giving acceptable performance. Since demulsifiers are surfactants this work was initiated in an attempt to apply surface chemical principals to emulsion breakers. Early in the work it was found that although much had been published about the stability of oil-in-water emulsions, very little was available about water-in-oil emulsions.