Using earlier results, as well as our own experiments, we have shown the existence of an optimum frequency in a demulsification process utilizing an AC electric field. Within a frequency range of 20 Ha to 100KHz we have determined voltage curves with different insulation and emulsions, these demonstrate why demulsification by means of an AC field is more efficient than that of a DC field. By analyzing the data obtained in measurement of dielectric properties of the system, we found that fmis about the same ofomegap instead of fp. To go Into it seriously, we concluded that the optimum condition is Tm=Tp, at which resonance occurs in the system and hence it promotes coalescence.