In this paper, a cognitive radio scenario composed of one primary (licensed) node and M secondary (unlicensed) nodes coexisting in the same spectral resource is considered. According to the commons model of cognitive radio, the secondary nodes are required to guarantee Quality-of-Service (QoS) constraints on the primary activity. Assuming a collision channel model, the stability region of the arrival rates at the secondary queues is investigated for given primary throughput and QoS constraints defined in terms of average delay of primary packets. Inner and outer bounds on the stability region are derived. The analysis is carried out at first for the case M = 2 and then generalized for any number of secondary nodes (M > 2), and is based on the concept of dominant systems. The results shed light on the impact of detection errors at the secondary nodes and of different levels of QoS requirements of the primary user to the achievable (stability) rate region of the secondary nodes. Numerical results suggest that the derived inner bound is a tight approximation of the real stability region.