Self-regulating network utilization is very important to the wireless network service providers to carry out new services such as wireless network gaming, which means that more users with a prepaid level of Quality of Service can be accommodated in a bandwidth limited network. However, in mobile ad-hoc wireless LANs, it is very difficult to regulate network utilization due to the time-varying nature of many important system parameters such as network load and channel quality. Moreover, the contention-based MAC protocols such as CSMA/CA adopted by IEEE 802.11 standard have been widely deployed in a wireless LAN environment for its flexibility, making self-regulating network utilization even more difficult. In this paper, we have proposed a fully distributed scheme running on each wireless station for self-regulating its network utilization to meet its prepaid service level. Simulation results show that the proposed scheme allows a wireless station to self-regulate the network utilization to its prepaid service level as close as possible by adapting the system parameters of MAC and PHY layers with changes of network environment such as the number of users and channel quality.