Wireless Body Area Network (WBAN) is a modern technology having a wide range of possible applications. The development scope of WBANs can diverse from hardware and applications design to network performance optimization. Reliability is a vital performance factor in WBANs. Body shadowing, environmental interference and inefficient routing can make a WBAN unreliable, which may severely affect the patient under observation. However, an opportunistic routing technique can improve the reliability via multihops by using opportunistic relays. We investigate the performance of opportunistic routing with two different path loss models for wearable WBANs, i.e., Log-normal path loss model and IEEE 802.15.6 Channel Model (CM) 3A. The performance metrics for the analysis include network lifetime, Packet Loss Probability (PLP), end-to-end (ETE) delay, and energy used per data packet. By using opportunistic routing with IEEE 802.15.6 CM 3A in comparison to Log-normal path loss model, reliability and energy efficiency are improved up to 16 and 25 respectively. © 2013 IEEE.