In Hybrid Electric Vehicles, Regenerative Braking is an essential function to convert vehicle kinetic energy into electrical energy, which charges the battery during a braking event to make a portion of captured kinetic energy available for use later. In comparison, conventional vehicles use friction brakes only and kinetic energy is dissipated as heat and not made available for later use. This paper introduces methods of evaluating Regenerative Braking Efficiency, including multiple efficiency definitions that lead to different attributes. The paper proposes regenerative brake event definitions during the FTP cycle and how they are used for control strategy and calibration updates. Also, we apply the efficiency metrics to four different vehicles from four automotive manufacturers for comparison. The paper presents a sample comparison result. Finally, we compare our efficiency metrics with the Environmental Protection Agency (U.S.EPA) official Brake Energy Recovery efficiency evaluation process.