Tensions between watercourse states are likely to escalate in the absence of effective legal frameworks by which to evaluate the impacts of large-scale unilateral water projects. Conscious of the need for such a framework, the lower Mekong River Basin States have developed the 1995 Mekong Agreement and related procedures for prior notification and consultation. The Xayaburi Hydropower Project constitutes the first project on the mainstream of the Mekong River that has been submitted to the consultation procedures under the 1995 Mekong Agreement. An analysis of the Xayaburi Project shows that both the design and implementation of the consultation process might be improved. The need to strengthen this process is particularly pertinent due to the numerous plans to further exploit the hydropower potential of the Mekong River and its tributaries. Additionally, examination of the prior consultation process under the Mekong Agreement offers valuable lessons for other international watercourses facing similar challenges.