This article assesses the effectiveness of the Mekong River Commission, its impact on the policies of its members, Thailand, Lao PDR, Cambodia and Viet Nam, and their engagement with the Commission. It also seeks to account for China’s influence on their cooperation, as China, the strongest upstream riparian state, is not a member of this cooperation scheme for the Mekong River basin. This is achieved using a model for explaining regime effectiveness which rests on the two main variables of problem malignancy and problem-solving capacity. Furthermore, the level of engagement of the riparians is accounted for by mainly two geographical variables: position on the river (upstream/downstream), and size of fraction of territory within the basin. (Manuscript received February 10, 2007; accepted for publication July 4, 2007)

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