We illustrate the effectiveness of using mobile sinks to obtain potential energy savings for the sensors during data dissemination in wireless sensor networks. The entire wireless sensor network is divided into two layers: the resource-constrained sensor nodes forming the bottom layer and a mobile ad hoc network of resource-rich sink nodes forming the top layer. Each sink node is assigned a particular cluster of sensors to monitor and collect data. A sink node moves to the vicinity of the sensor nodes (within a few hops) to collect data. The collected data is exchanged with peer mobile sinks and can also be transferred to a control center through multi-hop sink-to-sink data propagation. The energy loss due to multi-hop data propagation in disseminating the data from a sensor to the control center can be accounted to the sinks and not to the sensors. We also illustrate the effectiveness of using just one mobile sink to reduce energy consumption at the sensors in scenarios where one cannot afford to use multiple mobile sinks. In such scenarios, the mobile sink directly transfers the collected data to the control center.