Social dilemmas appear in two basic forms: the public goods problem (in which the individual must decide whether to contribute to a common resource) and the commons dilemma (in which the individual must decide whether to take from a common resource). The two forms of choice dilemma are equivalent in terms of outcomes, but because they involve different decision frames, they are not psychologically equivalent In this research, framing effects on decisions involving use of a common resource pool were explored in a 2 X 2 X 2 (Public Goods vs. Commons Dilemma Task Structure X Small vs.Large Group Size X Individualistic vs. Collective Social Identity) experiment. That the two versions of the decision task were not psychologically equivalent was evidenced both by a main effect of task structure and by interactions involving task structure, group size, and social identity. Overall, subjects kept more of the common resource for themselves under the public goods version of the task than under the commons dilemma frame. Furthermore, under the commons dilemma structure, group size had no effect on choice behavior, but in the public goods version individuals in large groups kept more than did individuals in small groups. Lastly, as the resource pool was depleted, the social identity manipulation had opposite effects for large groups under commons dilemma and public goods frames.