Cooperative game theory is a useful tool for determining if increased benefits exist for transboundary river basin stakeholders through cooperation in water resources management. Cooperative game theory has been used in many applications of water resources management including cost allocation from water development projects, cost allocation of regional wastewater treatment and transboundary water resources management. This research applies cooperative game theory to a water management in the transboundary Rio Grande/Bravo river basin located in North America. A cooperative game was created using a water management scenario which includes some of the largest irrigators in the United States and Mexico as players. This water management scenario is designed to improve water availability to the irrigators as well as considering environmental flows in the basin. Environmental flows account for the importance of flow variability to the health of an ecosystem and attempt to capture this flow variability as a range of flows which account for seasonable variability, magnitude, timing, frequency and the rate at which these flows change. Cooperative game theory is used to quantify the potential increase in benefit to the players and define a negotiation range for each player.