A relay network composed of a source, a set of relays, and a destination is considered. A queueing framework is proposed, where each node maintains a buffer to store its incoming traffic. An optimization-based formulation is proposed to maximize the mean service rate of the source queue. The relay selection technique is based on the statistics of the system parameters. Three packet decoding strategies at the relays are investigated and their performance is compared. The proposed decoding strategies, which do not require the channel state information at the transmitters, can outperform the max-max relay selection strategy.