This guideline discusses the effects of operating a rotodynamic pump at rates of flow greater than or less than the rate of flow at the pump?s best efficiency point (BEP). These effects influence the power consumption and life of pump components and, therefore, considering the operating rate of flow is essential to reliable, efficient pump operation. The preferred operating region (POR) and the allowable operating region (AOR) are defined for rotodynamic pump types and related to specific speed. Factors that affect AOR are discussed and NPSH margin versus rate of flow is presented. The guideline also indicates when stable or unstable operation may be expected based on typical system head curves, for pumps exhibiting a drooping head curve or a head curve with a dip. Considerations such as the robustness of a pump are also discussed.