In this study, common-pool resource experiments were carried out to analyze the efficiency of two simple, imperfectly enforced collective property-rights allocation rules. The design of the property-rights regimes in our experiment is based on both informal real-world arrangements practiced in the communal areas in our southern Namibian study site and the procedure used by the Namibian government, where communal farmers are granted access to resettlement farms according to their prior use of the commons. Our results suggest that in the short run the introduction of collective property rights increases the economic returns and has positive ecological effects, but that the unequal distribution stimulates inequality aversion, which diminishes the positive effect in the long run if the rules are only imperfectly enforced. We also find evidence for spiteful behavior, as a substantial fraction of subjects destroy the others’ grazing area, even though this has negative payoff consequences for the person who behaves spitefully.