 By requiring that cooperation of others always strictly benefits each player, the Schelling and Molander formulations of the \(n\)-person PD fail to model the surplus cooperation/free rider phenomenon that seems to infuse many of the tragedy-of-commons examples. Their conditions might, however be a plausible model for certain public good dilemmas. It is not unreasonable to suppose that any contribution towards public health, national defense, highway safety, or clean air is valuable to all, no matter how little or how much we already have, but that the cost to each for his own contribution to those goods always exceeds the benefit that he derives from that contribution. A particularly simple game meeting the conditions above is the public goods game. Each player may choose to contribute either nothing or a fixed utility C to a common store. Contributions to the store are added together, mutiplied by some factor greater than one, and divided equally among the members of the group. In this way a player benefits by same amount from the contributions of others whether she contributes herself or not, and loses by the same (smaller) amount from her own contribution whether others contribute or not. This is not true of PD's in general, though it is true of the exchange game mentioned in the introduction.