Study of liquid-liquid flow patterns in reduced dimensions is relevant under the current trends to miniaturize process equipment. The phase distribution results from interplay of surface (dominant in microchannels) and gravity forces (dominant in larger dimensions). The proposed analysis, based on minimization of total system energy comprising of kinetic, surface, and potential energy, unravels the influence of wetting properties and predicts the range of existence of annular and plug flow as well as the onset of stratification with increasing conduit dimension. Unlike existing models marking abrupt transitions, the proposed methodology can predict zones of transition where interfacial distributions gradually evolve with change of operating conditions-the predictions agreeing closely to experimental and literature data. The analysis illustrates the coupled effect of diameter, contact angle, and inlet composition on flow distribution and defines the transition from macrodomain to microdomain (millichannels) in terms of Bond number as 0.1 < Bo < 10. (C) 2015 American Institute of Chemical Engineers