In this paper, I study the ability of group members to cooperate against an incumbent in a repeated rent-seeking game and where group members and the incumbent have di¤erent valuations of the prize. I …rst consider that group members use Nash Reversion Strategies (NRS) to support cooperative behavior and show that full cooperation within the group is more easily sustained as a Stationary Subgame Perfect (Nash) Equilibrium (SSPE) as either group size, or the heterogeneity in the valuation of the prize, increases. In turn, I show that full cooperation within the challenger group can also be sustained as a Weakly Renegotiation-Proof Equilibrium (WRPE). Yet, an increase in group size makes it more di¢ cult to sustain within-group cooperation but an increase in the relative valuation of the prize by group members still facilitates group cooperation.