At the request of Rotterdam Energy Company Ltd, a subsidiary of the global electrical power company Intergen, CE examined the environmental profile of combined heat and power generation (cogeneration). To avoid over-estimation of potential macro-level savings, because of temporary or structural mismatches between heat and power demand, for example, a distinction was thereby made between the local and national level. The study shows that at the macro level new plant equipped with the best available technology (BAT) leads to approximately the same savings as the current average (about 30%). The extra savings achieved by cogeneration instead of separate heat and power production are a factor 10 less (several percent only). Because local authorities often employ poor indicators for CO2 emissions (viz. overall conversion efficiency) the study elaborates several indicators that providing optimum insight into the macro-effects of individual facilities. The study concludes that while there are still environmental gains to be achieved by constructing co-generation plant, these will be of limited additional value. More effective environmental gains are to be realised by creating incentives for actually implementing BAT and decommissioning out-moded plant.