Waste oil emulsions are generated in several manufacturing processes. Such emulsions not only affect the efficacy of wastewater treatment but also influence the water quality of the effluent. Thus, many processes have been developed for demulsifying such materials and salt-assisted microwave irradiation has been shown to be most effective in this respect. In the present study, we propose that artificial seawater can be an economical source of the cations required in this process, termed seawater-assisted microwave demulsification. Our experiments include tests of emulsion characteristics and the effects of microwave operating conditions on demulsification rate and separation efficiency of three oil-in-water (O/W) emulsions. We conducted batch demulsification tests on 50-mL aliquots with an initial oil content of 10 g/L, and found that the separation efficiencies of a cutting-oil emulsion, an olive-oil emulsion, and a cutting-oil/olive-oil mix reached 93.1%, 92.6%, and 93.2%, respectively, using our optimum operating conditions, which were 40s of microwave irradiation at 700W, a 60 min settling time, and addition of 12%, 32%, and 20% (all v/v) of artificial seawater, respectively. Using this set of operating conditions, a decrease in solution pH was found to significantly increase the demulsification efficiency after addition of inorganic acid, whereas an increase in the concentration of surfactant, sodium dodecyl sulfate (SDS), resulted in a decrease in efficiency. In addition, our test data were explored using a stepwise regression method, yielding a multivariable equation. This empirical equation was able to describe separation efficiency rather well, after exclusion of tests showing separation efficiency below 40%. (C) 2010 Elsevier B.V. All rights reserved.