A mathematical description of non-Newtonian fluids, in particular, emulsions, is of special importance now that most of the enhanced oil recovery methods are being modeled in increasing detail. Only recently a few characteristics of emulsion flow have been incorporated in some of the simulators. Nearly all enhanced oil recovery processes involve emulsion formation and flow in some form or other. Representation of such flow in mathematical models is still inadequate. This paper investigates the rheology of emulsions, their formation in porous media, and subsequent flow, from a mathematical standpoint. A critical evaluation of several models describing the flow of pseudoplastic fluids in porous media is presented. The models are expressed in a unified form that makes it possible to detect differences between the various models. The assumptions underlying the various models are discussed in detail. Furthermore, the paper gives a summary of the rheology and in situ formation of emulsions, and the role of a variety of other factors responsible for emulsification in porous media. The paper concludes with suggestions for incorporating emulsion flow in reservoir simulators. Extension to non-isothermal conditions is also discussed.