The use of the Clean Development Mechanism (CDM) is increasingly widespread in developing countries. However, CDM projects are still far from being an effective development activity due to the uneven distribution of these projects in a few relatively well-off economies. One potential cause of this imbalance is analysed in terms of the trade relationships between developed and developing countries. By applying a gravity model to a panel dataset, well-established export flows from developed economies towards developing countries are shown to explain why a large proportion of CDM projects are unevenly geographically distributed. This kind of lock-in effect regarding the CDM between developed and developing countries could be avoided by both enhancing the institutional framework in developing countries that host CDM projects and reinforcing compulsory rules for CDM destinations in the least-developed economies.