In today's scenario, both in gasoline and diesel engines, it is important to reduce power consumed by the auxiliary devices causing parasitic loss. Oil pump is one such device, used for lubrication purpose, which consumes higher power developed by the engine causing parasitic loss. Conventionally gerotor construction pumps are predominantly used in majority of engines, owing to its simpler construction, lower NVH and cost. However, this type being a positive displacement pump, consumes higher power with increase in speed. Hence, variable displacement oil pumps are gaining importance as the oil flow rate can be varied over the entire engine operating range. In this work, basic design elements of variable displacement oil pump are identified followed by building of mathematical model to calculate the critical design parameters. The basic mathematical model built can calculate oil flow rate, leakage losses and power consumption at different speed and load conditions. Proto samples were also built and tested at steady state conditions at different speed and load conditions. Results obtained shows that the mathematical model can predict the performance with in an accuracy of 5%. Hence, the developed mathematical model can be used as a tool for optimizing the design to achieve the target flow requirement with least power consumption. © 2019 SAE International. All Rights Reserved.