Wireless Sensor Networks (WSNs) are essential for numerous applications such as smart infrastructure, industrial automation, and environmental monitoring. However, improving energy efficiency, reducing transmission delay, and enhancing throughput remain significant challenges, particularly under realistic wireless conditions characterized by transmission errors. This paper introduces an energy efficient cooperative Medium Access Control protocol that enables source nodes to select the most suitable relay node to assist in data transmission. The proposed protocol adopts a cross-layer approach, where relay selection is optimized based on key factors such as residual energy and transmission time, ensuring more efficient and reliable communication paths. To evaluate protocol performance under practical conditions, an analytical model incorporating channel error probability is developed using a twodimensional Markov chain framework. The protocol’s effectiveness is assessed through simulations and compared against conventional methods, including IEEE 802.11b and BTAC. Results demonstrate the effectiveness of the proposed cooperative protocol by improving network performance, achieving better energy efficiency and throughput while reducing packet delivery delay.