measurement of electrochemical impedance spectroscopy used in situ is a suitable technique for the characterization of oil and water-in-oil emulsions. Nyquist diagrams for dehydrated oils are characterized by the formation of one semi-circle. The equivalent circuit proposed for the dehydrated oil is a resistance and capacitor (ROCO) in parallel. The resistance and conductivity of the oil calculated by impedance were 2.96 Gohm and 486 nS m(-1), respectively. Nyquist diagrams for the system composed of water emulsions in oil are mainly characterized by two semi-circles with different relaxation for oil and water-in-oil emulsions. The equivalent circuit is formed by RO and CPEO in parallel and in series with the arrangement of RW/O and CPEW/O in parallel, where RO and CPEO represents the oil, and RW/O and CPEW/O represents water-in-oil emulsions. The resistance of oil (RO) and water-in-oil (RW/O) emulsions increase with the increasing amount of water in the preparation. The increase in resistance shows that the emulsions become more stable with the addition of water. This result is consistent with the formation of rigid films on water-oil interfaces. The impedance measurements were applied to the analysis of the demulsification of the water-in-oil emulsions under an electrostatic field. (C) 2011 Elsevier Ltd. All rights reserved.