Summary The Energy Efficiency Index (EEI) offers the possibility, to rate the efficiency of a booster station by taking a load profile into account. Besides the quality of the used single machines, the EEI is massively depending of the applied operational strategy. For most operational points different numbers of pumps are able to cover the actual load, but for only one of these scenarios the energy consumption becomes minimal. This paper presents an approach for calculating the maximal attainable EEI for booster stations from the characteristics of the machines. Only the data of the single pump unit within the booster station is needed to calculate the EEI of an optimally operated booster station. The result of the optimization program is the optimal operational setting for every point of the load profile and thus the best achievable EEI. Furthermore we use this approach to make proposals for possible improvements for the control and topology of booster stations.