This paper presents the application of optimal control to two series-parallel hybrid architectures. The dynamic Programming method is applied to Toyota Hybrid System (THS) and Electrical Variable Transmission (EVT). First the theoretical approach of dynamic programming and its application to SP_HEVs is presented. The way to take into account the extra degree of freedom, provided by the decoupling of wheel and engine, is presented. Then, the optimal fuel consumption of the two architectures is compared on different drive cycles on the case of a same reference vehicle Prius II. Considering an over consumption of the EVT, a gear is inserted on the engine shaft. Finally, a parametric study shows that choosing the good gear ratio can reduce the EVT fuel consumption compared to those of the THS architecture.