In this paper, the electrical conductivity measurements of four types of crude oils at reservoir conditions were carried out using an in-house-developed pressurized cell. The newly introduced apparatus has the capability of performing electrical conductivity measurements of various reservoir fluids at high-pressure, high-temperature (HPHT) conditions. The cell can be pressurized with an inert gas to be far enough above the bubble points (P-b) of crude oils. The alternate voltage (AV) cycle methodology was applied to perform the experiments. In this method, the subtraction of electrical currents when the voltage alternated between two specified values (0 and 2 V in this work) was used to calculate the conductivity. The reliability of the methodology and equipment in making conductivity tests has been verified by comparing the conductivity results to the rest conductivity values measured via a standard method. Variation of crude oil electrical conductivity showed a strong relation to the physical and chemical properties of the reservoir fluids, including the electrical nature of compounds in oils and viscosity of fluids. The experimental data were fitted well to the Arrhenius model with a clear break point at a certain temperature for each oil, which can be linked to the structural change of the fluids at the mentioned temperatures.