This dissertation presents the evaluation of the energy efficiency of a series hybrid electric vehicle through the theoretical development of two electric propulsion systems and an experimental study of fuel consumption of the original vehicle. The experimental analysis was done by a test setting, consisting mainly by a chassis dynamometer, an autopilot system and a fuel flowmeter, all connected to the data acquisition system. In this study it was developed two theoretical models of propulsion systems for HEV. The first one consists of four in-wheel motors and the second one consists of two in-wheel motors on the rear axle. There are various methods for embedding a motor in the wheel. It is necessary to consider the weight, power and transmission efficiency. In the theoretical model it was considered a cycloidal reducer, which allows a reduction of 3:1 to 119:1 in one stage with an efficiency of 93 percent, together with a brushless DC motor, which has a high power density. The results of the evaluation of the electric propulsion systems show that the model with four in-wheel motors is more efficient than the model with two in-wheel motors. This is a consequence of the fact that the second model is heavier, because it needs a bigger amount of batteries and more robust motors. In the evaluation of the HEV energy consumption in comparison with the original gasoline model, it was observed interesting results regarding the energy savings. The HEV presents better performance in urban cycles that in road cycles, saving 57,6 per cent of the consumed energy in urban cycles and 11,4 per cent in road cycles.