In ad-hoc networks, cooperative diversity is especially desired where the use of multiple antennas may be impractical due to the size of nodes. There has been a lot of work on improving the peer-to-peer link quality by using advanced coding or power and rate allocation between a single source node and its relays. However, how to efficiently and fairly allocate resources among multiple users and their relays is still unknown. In this paper, a novel multiuser cooperation protocol is proposed, where multiuser diversity scheme is adopted to schedule different source/destination pairs and each pair computes its required rate based on a power reward. Power reward is adopted by each node to evaluate the power contributed to and by others so as to guarantee fairness. It will be shown that in energy-constrained cooperative ad-hoc networks, fairness can actually bring significant throughput gains. Simulation results will validate our analysis and show that compared to direct transmission and full cooperation protocols, much higher aggregate throughput can be achieved by the proposed Fair Cooperation Protocol thanks to improved fairness.