Theoretical and experimental studies were made to determine the effects of numerous system and component parameters on the magnitude and frequency of pressure surges which occur upon opening or closing a valve in a hydraulic system. It was found necessary to consider the system as a composite unit, due to the complex manner in which the effective resistances, inductances, and capacitances of the system components affected surge characteristics. Electric analogs have been proposed as a convenient means for system analysis, and theoretical approaches for their practical application have been developed. Analytical studies of existing and experimental data were made to determine the effect of pressure surges on the fatigue characteristics of various hydraulic system components. These studies indicated the magnitude of the surge to be of primary concern, with frequency and rate of pressure rise showing only secondary effects. Secondary high-frequency oscillations were found particularly undesirable because of their excessive peaks, but certain information pertinent to their control has been obtained.