In this paper, the energy consumption shares of plug-in hybrid vehicles (PHEVs) for electricity from the grid and conventional fuel depending on electric driving range are estimated. The resulting mobility costs and greenhouse gas (GHG) abatement costs per vehicle kilometer for the year 2030 are calculated and optimal electric driving range (which indicates the size of the battery) is found for different oil price levels with the help of a MATLAB based model for a typical compact passenger car (e.g. VW Golf). The results show that the optimum electric driving range for minimum mobility costs of a PHEV is between 12 and 32km. Furthermore, optimum GHG abatement costs are achieved with an electric driving range between 16 and 23km. These results are considerable lower than most market ready PHEVs (electric driving range of 50 to 100km), which shows that the automobile industry should concentrate on shorter electric driving range for PHEVs in the near future to offer cost optimum mobility and low GHG abatement costs. However, the oil price level and the consumer driving habits impact heavily on the cost performance as well as the optimum electric driving range of plug-in hybrid vehicles.