Hybrid cars are a very interesting option for consumption and pollution reduction in urban areas, as they allow to reduce part load operation of the engine. The hybrid operation is based on the combination of two power sources, and it is well known that a sensible choice of the power split strategy can strongly influence the total consumption as well as the emissions. Therefore, control design is usually considered a critical issue. This paper, however, argues that it might be better not to fix a control structure, but to state the problem in terms of an optimization problem, without an a-priori control structure, and that this leads to better estimates of the achievable targets and in this way to better control results. Copyright © 1999 Society of Automotive Engineers, Inc.