Abstract In this paper, the electrical conductivity of crude oil (S.G.= 0.9) is examined over the temperature range of 50 °C to +75 °C. It is shown that the conductivity of the oil increases exponentially with increasing temperature. Two possible conduction processes based on semiconductor theory and electrokinetic theory are discussed. Conductivities of the order of 2.5 ×10−8υm−1 were observed and the energy gap or activation energy was about 1.0 eV. Introduction With the wide use of electrical logging and the future possibility of the use of electrical heating methods for the extraction and processing of crude oil, detailed knowledge of the variation and nature of its electrical conductivity is required. To date, work seems to have been done on an ad hoc basis and very little has been published (1,2). The present work was performed On a variety of heavy crude oils (S.G. = 0.9) as extracted, because it is in this state that the oil is first encountered. No attempt has been made to explain the variations encountered for oils from different sources, as each sample followed a similar pattern. Later work will correlate changes in carrier concentration and mobility with chemical composition and the source of the oil. Experimental Method The apparatus consisted of two polished circular stainless steel plates, each 100 cm2 in area, spaced 1 cm apart in a perspex holder. The sample oil was poured on top of the lower plate and the upper plate was pressed into position in the holder, pushing some oil into the reservoir provided. The sample was kept in a nitrogen atmosphere to prevent excessive oxidation. The apparatus was installed in a temperature-controlled oven-refrigerator in which the temperature could be varied from −100 °C to + 400 °C, and a thermocouple was installed on the lower plate. The oven was set at a particular temperature and a series of current measurements were made on the sample for a variety of voltages. Some problems were encountered with initial changes in the results. These appeared to be due to the fact that the oil took an appreciable time to make intimate contact with the electrodes. This settling down period was considerably shorter at higher temperatures. A period of two or three hours was allowed for equilibrium to set in after each temperature change. The temperature range used was from −50 °C to +75 °C, because below −50 °C the resistance of the oil becomes too high to measure with the present apparatus with any reasonable degree of accuracy. At about +100 °C the various oil specimens became volatile, with a tendency to boil, and the results were not consistent. The apparatus was carefully and scrupulously cleaned and dried between each specimen change. Experimental Results and Analysis Initial results at 25 °C showed no change in resistivity with changing voltage or with changing the polarity of the electrodes after various periods of time. This means that the conduction process through the oil is not sensitive to the electrical field applied, at least not from 0 Vm−1 to 10 kVm−1.