to horizontal well applications is that the casing is conventionally used as the return electrode the electrode length can be comparable to the length of the return electrode the well casing thus the spreading resistance of a barren formation near the casing would dissipate about as much power as the oil bearing formation near the horizontal electrode thereby wasting power this inefficient design for long electrodes is overcome by the use of the iterated electrode design approach one solution is illustrated in fig1 where a heating electrode may also serve as a return electrode in the horizontal borehole for illustrative purposes only one pair of electrodes are shown in fig1 but additional pairs are usually employed as shown in fig2 another advantage of using the symmetrical excitation illustrated in fig1 and 2 is that each electrode pair exhibits about twice as much spreading resistance as for the monopole arrangement used in vertical wells where each heating electrode in the reservoir is shorter than the return current electrode such as the well casing to realize this advantage the geometry of all heating electrodes should be about the same and the voltage applied to one of the electrodes should be of opposite polarity of that applied to the other electrode of the pair this can be done simply by not grounding the output terminals of the power source or of the transformer that supplies power to the wellhead thus by using dual excitation.