This paper presents a systematic design approach to synthesize feasible configurations of parallel transmissions for a hybrid electric vehicle using single electric motor/generator. Based on the studies of existing parallel hybrid systems, four main types of parallel hybrid transmissions are classified and studied. The mechanisms, which were studied in present research, are two degrees of freedom compound planetary gear trains consisting of two simple planetary gear trains. By applying the proposed design approach, twelve feasible mechanisms for parallel hybrid transmissions are generated. Then, four potential mechanisms, which are used in existing designs, are employed to systematically synthesize 37 corresponding feasible parallel hybrid transmissions, including some existing parallel systems. To demonstrate the feasibility of the synthesized systems, a new parallel hybrid transmission is taken arbitrarily as a numerical example to illustrate its working principle with operation modes, and kinematics and power flow analysis. (C) 2015 Elsevier Ltd. All rights reserved.