This article compares the political economies of water and oil conflicts. It suggests that the ‘common pool resource’ (CPR) framework only partially explains the prototypically ‘upstream-downstream’ disputes over flowing water and oil ‘flows’, as CPR rivalry stems from users’ inability to exclude each other, while water and oil conflicts stem from certain users’ ability to exclude others. Yet, it also argues that key differences, related to the exclusivity of upstream sovereignty over resources, the ecological or economic nature of ‘downstream’ flow benefits, the practicality of ‘upstream’ flow control, and the size of the political benefits of gaining and exerting ‘upstream’control relative to its high economic costs, make ‘water war’ much less politically economic than oil conflict.