Energy-efficiency has become one of the major issues for mobile devices as these devices rely on their batteries. In this paper, we aim to reduce the energy consumption of mobile devices in wireless networks by maintaining mobile stations in the doze state as much as possible, without degrading the expected throughput even in highly-dynamic channel conditions. In the proposed scheme, each station only makes use of its local information and does not cause any overhead on network. Therefore, the proposed scheme can be easily implemented without any changes on current IEEE 802.11 standard. Performance of the proposed scheme has been examined by numerical analyses and extensive simulations. The results illustrate that the proposed scheme is very efficient and reduces the energy consumption of stations under a wide range of contention levels.