This paper presents a performance analysis of best effort support over the MAC protocol proposed in the IEEE 802.16 standard. We focus on the uplink channel since it is the critical element for efficient delivery of services on demand to individual users (i.e., Best Effort service). We describe a modeling approach and derive the resulting analytical model. Such a model allows us to efficiently compute network throughput. We test this model by means of computer simulations which are also reported in this paper. Simulation results and theoretical computations showed a close agreement, thus validating the model.