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We developed an electric oil pump (EOP) and a control algorithm for automatic transmission (AT)-based two-shaft parallel hybrid electric vehicles (HEVs). The EOP capacity was designed based on AT oil pump test results, and the torque of the EOP motor was determined by considering the flow rate and efficiency calculated according to the operating temperature of the AT fluid. A control algorithm consisting of low, high, and middle speeds according to the HEV driving mode was proposed for the operation of the designed EOP. Control logic was proposed to reduce the EOP energy requirements in the middle-speed range, in which the EOP and AT oil pump operate together. We verified that this control method could reduce electric load while supplying the required hydraulic pressure.