We discuss a cooperation framework applicable for wireless access networks, in which wireless users compete for opportunistically available bandwidth with one another to satisfy each quality-of-service (QoS) demand. Our key concept is to encourage a user with low QoS requirement to provide its redundant bandwidth to another user requesting more bandwidth. The provider of bandwidth at this time can be a client at the next moment, and vice versa. Such cooperative exchange of bandwidth increases chances to satisfy QoS requirements. This paper shows how to incorporate our framework in wireless local area networks (WLANs), which is called TXOP (Transmission Opportunity) Exchange. TXOP Exchange enables flexible bandwidth exchange between compliant STAs in WLANs without any effect on the legacy access point and legacy STAs. In this paper, we particularly show how to implement the TXOP providing function in uplink WLANs and demonstrate how it works through simulation results.