This paper focuses on the improvement of fuel consumption, vehicle performance, and driving aggressiveness for Hybrid Electric Vehicles (HEV) using epicyclic power split transmission (PST). In this paper, three and four branch transmission system models are analyzed and implemented into two HEVs. The modeling of the hybrid electric vehicle performance is carried using the QSS Toolkit. The models for the two vehicles are built based on the same baseline vehicle with the same vehicle parameters but with different transmissions. The vehicles are simulated over typical driving cycles; New European Driving Cycle (NEDC) and USA Federal Test Procedure FTP 75. The HEV results are also compared against a conventional IC engine plus manual gearbox vehicle. Computer programs for the analysis of epicyclic transmission based on a matrix method are developed and used. The simulations show that the 4 branch epicyclic offers substantial improvements of reduction in energy consumption, though the benefits are sensitive to the driving cycle used.