Abstract: To propose a Reliable, Energy Efficient, Fault Tolerant (REEFT) clustering algorithm for aggregating sensor measurements in Wireless Sensor Network (WSN). It is a hierarchical algorithm in which energy efficiency is achieved by constructing static clusters with reliable cluster head based on distance. Lifetime of WSN is improved through solving the important issues in WSN, which are distribution of clusters, optimal number of clusters and number of nodes in a cluster and optimal time duration of clustering cycle. Also the algorithm include fault tolerance feature to tolerate the Cluster Head (CH) failure and improve the packet delivery ratio. The algorithm was tested using simulations and its performance improvements were analyzed.