We propose a Partnership-based Cooperative MAC protocol (PC-MAC) based on the Distributed Coordination Function (DCF) protocol in wireless networks. The contribution of this paper is twofold. First, we introduce a Cooperative InterFrame Space (CIFS) for latency reduction and second, we introduce a control frame called Request to Cooperate (RTC) for on-demand packet relaying for error recovery. We compare PC-MAC with the non-cooperative DCF protocol. The analysis results show that using cooperation improves the theoretical maximum achievable throughput and the saturation throughput.