Common pool resource (CPR) users face the risk of resource shortage if the sum of the claims they have over the common pool resource is incompatible with the actual resource size. However, in many situations, agents can diversify their resources and substitute an alternative safe resource but costly to a free but risky CPR. This paper adresses the original question of the interaction between the sharing rule of the CPR (required to allocate the available resource in case of shortage) and the resource diversification choices of agents. It also bridges the gap between the CPR and the bankruptcy litterature by measuring the performance of traditionnal bankruptcy sharing rules in CPR management. We find the optimal sharing rule and the optimal diversification choices under different assumptions concerning the group of CPR users: heterogeneity in valuation of the resource (under risk neutrality) and heteorogeneity in risk tolerance (assuming equal valuation). The first-best sharing rule, leading to optimal diversification level and greatest efficiency, is a rule which is independant of users.