In this paper, we propose a multi-band multi-channel adaptation algorithm to enhance the performance of single-hop mobile ad hoc networks (MANETs) running the IEEE802.11 standard. The algorithm takes into consideration medium contention, coverage range and obstacle penetration in selecting both the operating band and the channel within the selected band. Applying the algorithm, a MANET with its usual highly-dynamic behavior, in terms of mobility and number of active stations, seeks a better operating environment according to its real-time practiced performance within the surrounding environment. The algorithm operates independently on each MANET without any type of coordination with other competing IEEE802.11 networks. Simulations are performed to demonstrate the performance of the proposed algorithm. The obtained results show its feasibility in enhancing the performance of a MANET over the fixed band and channel allocation strategies of the IEEE802.11 standard.