This article addresses the conflict over the Euphrates and Tigris waters from the perspective of negotiation theories, by examining the role of power in upstream/downstream negotiations. Conceptual and empirical links are established between water, negotiation (structure, process), power (asymmetries, coalition dynamics, strategies, development of alternatives) and security (direct/indirect interests such as national security, border security, territorial claims, economic development and environmental concerns). The study concludes that asymmetries in power have favored upstream/downstream interactions towards bilateral if not basin-wide arrangements. The framework shows that traditional elements of power, such as upstream positions, military and economic resources, do not constitute the only sources of power. Bargaining power can also determine the dynamics between respective riparians. Time constitutes an important source of power, and interests vary over time when political settings and security concerns shift. Downstream or more vulnerable riparians can invert situations of power asymmetry by acting on the basin-dominant riparian's interests and thus reduce its alternatives. Syria's use of 'issue-linkage' in its interactions with Turkey over water and wider security issues serves as the primary example.