As the nodes have limited battery power in Wireless Sensor Networks (WSNs), energy efficiency and fault tolerance should be the two major issues in designing WSNs. However, previous studies on positioning base stations (BSs) in WSNs are focused on energy efficiency only. Yet, mission-critical applications like emergency medical care systems should be guaranteed continuous services considering fault tolerance. In this paper we propose to place multiple BSs considering not only energy efficiency but also fault tolerance. We present two strategies to find the optimal position of BSs; (1) minimizing the average transmission energy for energy efficiency; and (2) minimizing additional energy consumption after a BS failure for fault tolerance. The optimal positions for multiple BSs are derived by the metric that considers both energy efficiency and fault tolerance, with a weight factor. Our simulation results show that fault tolerance is important and strongly related to elongation of network lifetime. In addition, we show that our proposed scheme is more energy-effective than previously suggested strategies on unexpected environmental changes which occur commonly in WSNs and sustain the network lifetime effectively under BS failures.