Suppose state A controls some resource such as a rainforest and there are some other agents in the international system that wish to see this resource preserved. These agents are prepared to make a contribution towards sharing the costs of maintaining the resource. What would be the long term trajectory of the resource level under different programmes? What type of cost sharing programme would maintain the highest level of the resource? Which programme would give the best value for money for the contributing player? This paper attempts to answer these questions. This is done by examining a dynamic model with an infinite time horizon. (C) 2001 Elsevier Science Ltd. All rights reserved.