A detailed analysis on enhanced heating effects attributed to resonance of microwaves has been carried out to study the efficient heating methodologies for oil-water emulsions. Studies on heating have been carried out for samples incident with microwaves at one side and at both sides. The maxima in average power corresponding to resonances occur at various sample thicknesses for all emulsions and we consider two dominant resonance modes R-1 and R-2, where the average power at R-1 is larger than that at R-2. During one side incidence, it is observed that processing rates are greater at the R-2 mode for both oil-in-water (o/w) and water-in-oil (w/o) emulsions, whereas for both-sides incidence, the R-2 mode is favored for o/w emulsion and the R-2 mode is advantageous for w/o emulsion. The greater rates in thermal processing are observed when the emulsions (o/w and w/o) are incident at both sides. Current analysis recommends on the efficient way to use microwaves in a customized plane-wave oven for greater heating effects and determines the optimal sample thicknesses vs. various oil-water contents for thermal processing. The emulsion system is a combination of materials with very low dielectric loss (oil) and high dielectric loss (water), and the effective dielectric response is highly nontrivial to predict the efficient way to heat an emulsion, either o/w or w/o. (C) 2004 American Institute of Chemical Engineers.