Informational Power Through Pivotality: When a Hegemon May Choose Consensus

When does a powerful state prefer consensus to majority rule in an international organization? I develop a formal model of institutional design in which a hegemon has private information about the value of multilateral cooperation. Under majority rule, weaker states can form winning coalitions without the hegemon, so its private information has limited strategic value. Under unanimity, every agreement requires the hegemon's approval, forcing weaker states to decide how much to offer without knowing how valuable cooperation really is. This uncertainty works in the hegemon's favor: weaker states pay more than necessary to secure agreement, and majority rule eliminates this advantage entirely. In a calibration to OPEC circa 1986, the hegemon captures 28\% of the cooperation surplus under unanimity (9 percentage points above its outside option) compared to 23\% under majority (4 points above), a screening premium of 5 percentage points that majority rule eliminates entirely. This screening advantage means that, once cooperation is promising enough for weaker states to participate under unanimity, the hegemon strictly prefers it. Consensus, in this account, is not a concession to weaker states but an institutional arrangement that makes informational advantage politically productive---offering a distributive explanation for consensus rules in organizations such as OPEC.