Because of the low-power energy nodes used in a network, energy plays a pivotal role in the lifetime of wireless sensor networks (WSNs). This study elaborates on a routing method featured with optimum energy consumption in wireless sensor networks. Some of routing protocols with high energy efficiency (LEACH, Director Diffusion, Gossiping, PEGASIS, and EESR) were examined. We also looked through strategies of the protocol for WSNs such as data aggregation and clustering, routing, different node role assignments, and data-center methods. The routing protocols were compared regarding variety of metrics influencing requirements of the specific application and WSNs in general.