In this paper, we consider cooperative networks of users that implement an unselfish protocol to decode and forward packets of their partners. In unselfish cooperation, a user that has successfully retrieved the source data of a partner, will unconditionally assist that partner in its transmission to the destination. We use a threshold-based model to derive an analytical expression for the end-to-end packet error probability and we validate our approach comparing theoretical to simulation results. Furthermore, we explore the interplay between various network parameters, such as the number of users, the transmission scheme and the quality of the interconnecting channels, and we briefly discuss the impact of power allocation on the overall performance.