There is little evidence from impact evaluation studies of ambitious residential energy conservation programs, especially in developing countries. In this paper, I investigate the short- and long-term impacts of the most ambitious electricity conservation program to date. This was an innovative program of private incentives and conservation appeals implemented by the Brazilian government in 2001-2002 in response to supply shortages of over 20%. I nd that the program reduced average electricity consumption per customer by 25% over a nine-month period in affected areas. Importantly, the program reduced consumption by 12% in the long run. Such persistent effects, which arose mostly from behavioral adjustments, may substantially improve the cost-effectiveness of ambitious conservation programs. Finally, I show that a price elasticity estimated out-of-crisis would have to be increased fivefold to rationalize conservation efforts by the private incentives alone. Appeals to social preferences likely amplify consumers' responsiveness in times of crisis.