The road transportation sector is characterized at the moment by its being the most important energy consumer which is almost totally dependent on oil products. This will hardly change in the near future. The desirability of a rational use of energy is leading to an increase in the importance of urban public transportation. This is enhanced by some negative aspects of passenger car traffic in urban areas such as congested streets, parking problems, exhaust emissions, noise. If an oil substitution is to be aimed at, it can be seen that good possibilities for the introduction of alternative fuels are offered by the public transportation sector with its own vehicle fleets and own fuel supply networks. A comparison is given of three realistic alternatives for an implementation in public bus transportation. The propulsion systems chosen for the comparative investigation foresee the use of the following sources of energy: diesel, LPG and electricity. The paper deals with the energy consumption. These considerations are however not limited to the final energy consumption but also take into account the amount of primary energy required in each case. This enables a global statement to be made regarding the economics of the input of energy into different propulsion systems in urban public bus transportation.