We show that plurilateral agreements facilitate global tariff liberalization by creating
an MFN-based margin of cooperation that leaves preferential access via preferential
trade agreements (PTAs) unchanged. In a model of endogenous trade agreement
formation with farsighted governments, PTAs become rigid once exclusion or freeriding
incentives bind, constraining further PTA expansion. Plurilateral agreements
relax these constraints by allowing countries to liberalize selectively in a differentiatedgoods
sector without altering existing PTAs. As a result, the stable equilibrium trade
network consists of the PTAs that would arise absent plurilaterals, augmented—
but not replaced—by plurilateral MFN liberalization. This mechanism provides an
explanation for the growing role of sectoral plurilateral agreements within the WTO
as preferential liberalization becomes increasingly constrained.