The demulsification kinetics of water-in-oil (W/O) emulsions in a high ac electric field was investigated by using a batch cylindrical-demulsifier. The oil phase was liquid paraffin containing 1-10 wt% SPAN80 or ECA4360 as surfactant. The aqueous phase was deionized water containing 0-40 wt% H(2)S0(4) solution. The rate of demulsification was studied experimentally. The effects of emulsion structure and properties (water drop size, aqueous-phase electrolyte concentration, surfactant concentration, surfactant type) and demulsifying conditions (applied voltage, distance between electrodes) on demulsification rates are discussed. An empirical correlation is presented for estimation of the demulsification rate of W/O emulsions in a high ac electrostatic batch demulsifier.