The Customary International Law Supergame February 23, 200 dilemma-type circumstances, may achieve resolution despite theory. Elinor Ostrom u Observation suggests that even certain commons problems, or other prisoner states that "[a] substantial gap exists between the theoretical prediction that self- nterested individuals will have extreme difficulty in coordinating collective action and the reality that such cooperative behavior is widespread, although far from inevitable Ostrom cites considerable evidence regarding the amount and circumstances of cooperation by individuals in n-person collective action problems. The evidence show that individuals contribute to the resolution of these problems in substantially greater the evidence is obtained in circumstances where the assumptions of the prisoner p huch of amounts than the standard prisoner's dilemma model would suggest. Of course, dilemma are violated-by allowing individuals to communicate, enter into agreements and iterate play. We do not deploy any data in this article. However, we advance a plausible theory of potentially stable and efficient equilibria in the n-player prisoners dilemma, and suggest some possible approaches to empirical testing b. Choice of Strategy within the prisoners dilemma, we must postulate a particular strategy for states to play. There are many choices. We mention only three: tit-for-tat, grim trigger, and penance 1. Bilateral or multilateral retaliation An important aspect of the structure of the game pertains to the ability to impose sanctions in a discriminatory manner States may have trouble discriminating in the application of sanctions for several reasons. First, they may not be able to obtain information regarding the author of the violation. This might occur, for example, with respect to pollution at sea, or terrorist attack. Second, it may be costly for states to respond in a discriminating way. For example, if the sanction involves trade barriers, the sanctioning state must instruct its customs officers to discriminate among goods by origin. Third, and most important, the relevant good being produced by cooperation may be non-excludable. This would occur with the provision of public goods or the protection of international commons To the extent that states are unable to discriminate. their retaliation, if any, must be multilateral, instead of bilateral. This obviously limits the strategy that they are able to play and the relationships that they may enter into. Thus, given that the strategies available to a state are"cooperate"or"defect, there are at least two possibilities that we need to consider in connection with a multilateral game Elinor Ostrom, Collective Action and the evolution of social Norms, 14: 3 J ECoN PERSP.137,138(2000The Customary International Law Supergame February 23, 2004 13 Observation suggests that even certain commons problems, or other prisoner’s dilemma-type circumstances, may achieve resolution despite theory. Elinor Ostrom states that “[a] substantial gap exists between the theoretical prediction that self￾interested individuals will have extreme difficulty in coordinating collective action and the reality that such cooperative behavior is widespread, although far from inevitable.” 39 Ostrom cites considerable evidence regarding the amount and circumstances of cooperation by individuals in n-person collective action problems. The evidence shows that individuals contribute to the resolution of these problems in substantially greater amounts than the standard prisoner’s dilemma model would suggest. Of course, much of the evidence is obtained in circumstances where the assumptions of the prisoner’s dilemma are violated—by allowing individuals to communicate, enter into agreements and iterate play. We do not deploy any data in this article. However, we advance a plausible theory of potentially stable and efficient equilibria in the n-player prisoner’s dilemma, and suggest some possible approaches to empirical testing. b. Choice of Strategy Within the prisoner’s dilemma, we must postulate a particular strategy for states to play. There are many choices. We mention only three: tit-for-tat, grim trigger, and penance. i. Bilateral or Multilateral Retaliation An important aspect of the structure of the game pertains to the ability to impose sanctions in a discriminatory manner. States may have trouble discriminating in the application of sanctions for several reasons. First, they may not be able to obtain information regarding the author of the violation. This might occur, for example, with respect to pollution at sea, or terrorist attack. Second, it may be costly for states to respond in a discriminating way. For example, if the sanction involves trade barriers, the sanctioning state must instruct its customs officers to discriminate among goods by origin. Third, and most important, the relevant good being produced by cooperation may be non-excludable. This would occur with the provision of public goods or the protection of international commons. To the extent that states are unable to discriminate, their retaliation, if any, must be multilateral, instead of bilateral. This obviously limits the strategy that they are able to play and the relationships that they may enter into. Thus, given that the strategies available to a state are “cooperate” or “defect,” there are at least two possibilities that we need to consider in connection with a multilateral game: 39 Elinor Ostrom, Collective Action and the Evolution of Social Norms, 14:3 J. ECON. PERSP. 137, 138 (2000)