In the field of hydraulic drive technology various power supply systems are used within different power unit set-ups. The both of two mostly used drive concepts in modern electrohydraulic systems, a variable displacement pump driven by constant speed electric motor and fixed displacement pump driven by a variable speed electric motor, have some disadvantages, especially regarding the increasing demand for maximum efficiency of the entire power unit without lowering the high dynamics. The combination of a variable pump and speed-controlled electric motor, offers the option of setting two parameters of the drive, the rotational speed of the motor and the pump flow-rate. Such a combination allows all power unit components to operate within the areas of their maximum efficiencies, the so-called maximum efficiency drive. A prerequisite for designing suitable controllers that would ensure the operations of individual components within the areas of maximum efficiency, regardless of the current operating point, is certainly knowledge about the efficiency area of the entire power unit. This paper presents a procedure for determining areas of efficiency, first on the basis of simulation and detailed models of each component, and later verification of the model using an experiment.