Abstract The comparison of mechanistically different advanced oxidation processes (AOPS) UV/H2O2, UV/03 and O3/H2O2 needs a non-specific figure-of-merit to avoid influences by system-inherent parameters. The chosen figure-of-merit consists of the electrical energy per order of magnitude in oxidation per m3, EE/O. Results from own experiments were compared with data derived f rom the literature. Considered were batch-experiments, pilot-plants and full-scale plants. The combination O3/H2O2 proved to be the most efficient process by means of energy consumption irrespective of the size of the plant.