<p><b>Abstract</b>—This paper presents a fair decentralized mutual exclusion algorithm for distributed systems in which processes communicate by asynchronous message passing. The algorithm requires between <tmath>$N-1$</tmath> and <tmath>$2(N-1)$</tmath> messages per critical section access, where <tmath>$N$</tmath> is the number of processes in the system. The exact message complexity can be expressed as a deterministic function of concurrency in the computation. The algorithm does not introduce any other overheads over Lamport's and Ricart-Agrawala's algorithms, which require <tmath>$3(N-1)$</tmath> and <tmath>$2(N-1)$</tmath> messages, respectively, per critical section access and are the only other decentralized algorithms that allow mutual exclusion access in the order of the timestamps of requests.</p>