Two studies evaluated the effects of a group contingency on electricity conservation. In Study 1, residents of 166 apartment units in three towers held meetings and received biweekly payments of the value of electricity saved compared to predicted use. The group contingencies were initiated in each tower in a multiple-baseline design. The program produced substantial savings in one tower (11.2% of temperature-adjusted baseline), moderate savings in another (4.0%), and minimal savings in a third (1.7%). Overall, the residents saved 6.2%. In Study 2, residents of 255 apartment units, also in three towers, received the same treatment, except only 50% of the value of their savings were paid, and they received a one-time bonus of $5 for using >/= 10% less than baseline. Towers in Study 2 showed savings of 9.5%, 4.7%, and 8.3%, an average of 6.9%.