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To increase the end-to-end packet delivery ratio in lossy wireless sensor networks, existing routing protocols often use the data forwarding schemes based on a hop-by-hop ACK-based retransmission mechanism. However, these schemes may waste a considerable amount of energy for data transmissions, especially when the link quality is low for ACK transmissions. This paper proposes a novel probability-based data forwarding (PDF) scheme to minimize the energy consumption for unnecessary data retransmissions. In PDF, a retransmission threshold is set in each sensor depending on the probability of sending out a data packet successfully, thus becoming probability-based. The threshold is a number of data retransmissions sufficient for a data packet to arrive successfully at a next hop. The sender node stops sending a data packet after the threshold even if it does not receive an ACK message. Mathematical analysis and simulation results demonstrate that the proposed PDF scheme can save much energy and significantly increases the energy efficiency compared to the pure-ACK-based scheme when both schemes use the two well-known data forwarding metrics, PRR × Distance and NADV, in the network layer by up to 140.50% and 57.55%, respectively. [ABSTRACT FROM AUTHOR]