Purpose. Improvement of calculation accuracy of electric power losses in power supply systems of the oil and gas complex with reactive power compensation t losses, taking into account the largest power losses separately from th e active and reactive power transmission, has allowed increasing the accuracy of the energy loss determination. The method for determining the optimum capacity of compensating devices is proposed. Findings. The necessity of taking into account the form of charts of active and reactive capacities and the power of compensating devices during calculation of electric power losses in power supply systems is substantiated. It has been shown that the efficiency of reactive power compensation in order to reduce the power losses significantly decreases with high values of the power factor. Originality. The method of unregulated compensating devices optimum power calculation is proposed, provided the minimum power losses in the power supply system. The method of electric power loss calculation in power supply systems with compensating devices is improved by means of separate account of active and reactive power components during determination of the time of the largest losses, which allows increasing accuracy and reducing errors of calculations. The structure of the determination method of energy losses in the network is synthesized, which, unlike the existing one, allows taking into account the influence of the difference in the maxima of active and reactive load on the accuracy of calculations and optimizing the power of compensating devices. Practical value. Improved accuracy of calculation of electricity losses. Selection of optimal power of unregulated compensating devices, which corresponds to the minimum power losses in the power supply.