In two-player games with negative (positive) spillovers it is well-known that symmetric agents both overact (underact) at the Nash equilibria. We show that for heterogeneous agents this rule of thumb has to be amended if the game features strategic substitutability.

For simple economic models of transfrontier pollution, Chander and Tulkens (1995) and (1997) have offered a formula for transfers to sustain international cooperation on a voluntary basis and which deter coalitionnal free-riding under some reasonable behaviours of countries not in the coalition....

For simple economic models of transfrontier pollution, Chander and Tulkens (1995) and (1997) have offered a formula for transfers to sustain international cooperation on a voluntary basis and which deter coalitionnal free-riding under some reasonable behaviours of countries not in the coalition....