Sensor networks have recently gained a lot of attention from the research community. Sensors are significantly resource-constrained devices and last till the depletion of their batteries. Sensor networks typically have a large number of nodes. To ensure scalability sensor networks are often partitioned into clusters, each managed by a cluster head (gateway). Efficient management of a sensor network for extending the lifetime of the network is among the prominent areas of research in this domain. While most of the previous research focused on the optimal use of sensor?s energy, very little attention has been paid to the efficiency of energy usage at the gateway. Tasks need to be allocated to gateways in such a way that maximizes the life of these cluster-heads and eventually the whole network. In this paper, we present an optimization scheme for task allocation to gateways. The task allocation problem is modeled as a zero-one nonlinear program. Simulation results show that substantial energy savings can be obtained with the proposed method.