This paper presents and analyses a new near-optimum medium access control (MAC) protocol. The proposed access scheme is suitable for a CDMA mobile communication environment and minimises the total number of spreading codes needed to achieve a certain throughput. It also has a delay performance approaching that of an ideal optimum M/M/K system, where K is the number of spreading codes being used. The protocol is a free random access protocol when the traffic load is light and switches smoothly and automatically to a reservation protocol when traffic load becomes heavier. It is based on distributed queues and a collision resolution algorithm. Moreover, a physical receiver structure is proposed and analysed in order to preserve the robustness of the protocol in a wireless link. The results obtained show that the protocol outperforms other well known medium access protocols in terms of stability and delay, even when taking into account the loss caused by channel propagation conditions.