This paper analyses profitability and stability of international agree
ments to protect the environment in the presence of trans-frontier or
global pollution, Each country decides whether or not to coordinate it
s strategy with other countries. A coalition is formed when conditions
of profitability and stability (no free-riding) are satisfied. It is
shown that such coalitions exist; that they tend to involve a fraction
of negotiating countries; and that the number of signatory countries
can be increased by means of self-financed transfers. However, expandi
ng coalitions requires some form of commitment. Such schemes of commit
ment and transfers can even lead to cooperation by all countries.