The existence of a critical pressure ratio due to gas-dynamic choking is well known for an ideal gas. It is reasonable to assume that liquids whose compressibility is defined by the bulk modulus also have a critical pressure ratio. The problem discussed here is a fundamental one because it deals with the basic principles of the compressible flow of liquids. It has been shown that even though an ideal gas with a constant heat capacity ratio value has a critical pressure ratio, liquid with a constant bulk modulus value experiences a critical pressure difference. As the outlet pressure gradually decreases, the liquid reaches the local speed of sound, and further reduction of this pressure does not lead to an increase in mass flow. This phenomenon occurs in liquids without considering the change from a liquid to a gaseous phase. Behavior is confirmed analytically for different bulk modulus models, and for a constant bulk modulus value, the phenomenon is verified by numerical simulation using computational fluid dynamics. The conclusions published in this work point to striking analogies between the behavior of liquids and ideal gas. The equations governing the motion of liquids derived in this work, thus complete the fundamental description of the critical flow of fluids.