Wireless ad-hoc sensor networks differ from wireless ad-hoc networks from the following perspectives: greater energy constraint, light weight routing protocols, and flexible communication patterns. This paper proposes an energy aware routing protocol (EARP) and presents an analysis for energy consumption in various phases of route discovery and maintenance. Based on the energy consumption associated with route request processing, EARP advocates the minimization of route requests by allocating dynamic route expiry times. This paper introduces a unique mechanism for estimation of route expiry time based on probability of route validity (Proute-valid), which is a function of time, number of hops and mobility parameters. In contrast to AODV, EARP reduces the repeated flooding of route requests by maintaining valid routes for durations longer than ten seconds as fixed by AODV.