Hybrid vehicles offer a potential for significantly reduced fuel consumption and emissions during normal operation, because for the scope for operating the prime mover at its optimum, and the ability to meet sudden power demands from a combination of the prime mover and stored energy. Hybrid vehicles can also operate with 'zero emissions' in sensitive urban environments. Thus despite the extra cost associated with hybrid vehicle systems, then there will be circumstances in which the increased capital cost is justified. Indeed Toyota sell such a vehicle (Prius) in Japan, with imminent release in Europe and North America. Parallel and series hybrid configurations are well established, and ADVISOR has been used to demonstrate the fuel economy benefits of hybrid vehicles compared with conventional vehicles. ADVISOR is a simulation package developed by the NREL for the US DOE, that runs in the MATLAB environment, and uses SIMULINK for establishing the control strategies. ADVISOR is a remarkably versatile package, in that it allows the user to define the performance maps of the elements in the hybrid vehicle, and by re-programming to implement new sub-models and control strategies. Indeed this is necessary for modelling the Toyota Prius hybrid vehicle, since this uses a Dual Hybrid system that combines features of series and parallel hybrid operation. A medium sized passenger car has been modelled for operation on the extended European drive cycle and comparisons have been made between conventional vehicles and the different types of hybrid vehicle. (Author)