During low user demand, significant energy can be saved in a cellular network by using base station switching (BSS). However, coverage restrictions limit the number of base stations (BSs) a cellular operator can turn off. In this work, we examine the scenario when multiple cellular operators cooperate by sharing the load of their users with BSS (for example, on weekends). We show that significantly more energy can be saved by performing BSS with load sharing between the cellular operators. We formulate this cooperative BSS as an optimization problem. Further, for suitable service level agreements between the cellular operators, we show that the proposed optimization problem is real time solvable. Finally, we present results that quantify the achievable gains obtained by BSS with cooperation among the cellular operators. We also present the rate and coverage trade-off results which can be used by the cooperative cellular operators to find suitable points of operation. © 2016 IEEE.