The aim of the article is to look at the possibility of accurately determining the energy efficiency of drive systems. The results of experimentally determined efficiencies and the efficiencies determined from simulations of two hydrostatic systems with throttling control and fed by a constant capacity pump were compared. The research apparatus was very precisely designed, made and automated. The measuring instruments that were used are characterized by their high measuring accuracy. The issues related to the determination of the energy losses and the energy efficiency of the hydraulic motor or drive system, which should be determined as dependent on the physical quantities independent of these losses, were also discussed. A Paszota diagram of the power increase in the direction opposite to the direction of the power flow, replacing the Sankey diagram of the power decrease in the direction of the power flow in the hydraulic motor or in the drive system, was analyzed. The results showed that a Paszota diagram opens up a new perspective on research on the power of energy losses and energy efficiency of hydraulic motors and drive systems.