Mobile ad hoc networks have very attractive intrinsic qualities. However they will be adopted only if they are able to support applications with QoS requirements. They should provide a route providing the QoS requested by a flow. The OLSR routing protocol can be extended for that purpose. OLSR relies on multipoint relay (MPR) selection that has an important effect on the routing protocol's performances. Indeed, the overhead generated by the OLSR protocol and more particularly the flooding efficiency depend on MPR selection. Moreover, MPRs are used as intermediate nodes in the routes. The analysis of MPR selection presented in this paper, gives quantitative results and also takes QoS support into account. Simulations on large and dense networks show that our analysis is highly accurate.