Microwave oven heating rates of various oil-in-water emulsions, water-in-oil emulsions, and layered systems were compared. Emulsions heated faster than corresponding layered systems, which heated faster than a calculated weighted average of individual components. Differences were attributed to increased power absorption caused by the large number of interfaces occurring in emulsions, or by a single interface in the layered system, and by resonant absorption of microwave radiation, which is determined by dielectric properties. The types and proportions of emulsions determined the number of interfaces. The dielectric properties and sample size determined in which samples resonant absorption occurred.