Multirate opportunistic routing was proposed to achieve high throughput by exploiting multi-user diversity and transmission rate diversity in wireless networks. However, the performance of multirate opportunistic routing still cannot be guaranteed when participating nodes are contributed by different parties and thus have selfish behaviors. In this paper, we present the first Cooperation-Optimal protocol for Multirate Opportunistic routing and forwarding, namely COMO, which guarantee the faithfulness of each player, and thus achieve the social efficiency and strongly Pareto efficient Nash equilibrium with the faithfulness as a given property. Here, social efficiency means that the end-to-end throughput should be maximized, while in a strongly Pareto efficient Nash equilibrium, no one can improve her utility without decreasing the utility of at least one other player. We not only rigorously prove the game-theoretic properties of our incentive protocol, but also extensively evaluate its performance on the ORBIT wireless testbed. Experiment results show that our protocol can prevent participating nodes' selfish behaviors and guarantee high performance of the multirate opportunistic routing protocol with a low communication overhead.