This paper develops methods to measure the impact of conservation programmes on electric utility earnings.The methods are applied to two case studies. Detroit Edison represents a case where impacts are unfavourable. This utility has 'excess capacity' which is only made worse by conservation. Pacific Gas and Electric represents a case where conservation helps defer the need for new capacity. Even in this case, programmes targeted at summer peak demand are more beneficial than those which save baseload energy. Conditions determining the earnings impact of conservation are complex, involving regulatory factors that are specific to individual utilities.