Compensating the cooperators: is sorting in the prisoner's dilemma possible?

Choice between different versions of a game may provide a means of sorting. We experimentally investigate whether auctioning off the right to play a prisoner's dilemma game in which the cost of unilateral cooperation is lower than in the status quo version separates (conditional) cooperators from money maximizers. After the auction, significantly more subjects cooperate in the modified PD than in the status quo PD, whereas there is no difference between cooperation rates if the two versions of the game were assigned to participants. However, sorting is incomplete and cooperation deteriorates over time.