Energy efficient and reliable data forwarding becomes important if resources are limited such as in Wireless Sensor Networks. In this paper, we discuss how the error rate associated with a link affects the overall probability of reliable delivery, and consequently the energy associated with the reliable transmission of a single packet. The analysis includes both fixed-power and variable-power scenarios along with the End-to-End Retransmission (EER) and Hop-by-Hop Retransmission (HHR) techniques. In the EER case, a threshold value for the packet error rate at which both scenarios will result in the same energy costs is defined. The relation between this threshold value and the difference in number of hops between both scenarios is also derived. The simulation results finally confirm the theoretical model.