We consider price-fee competition in bilateral oligopolies with perfectly-divisible goods,
non-expandable infrastructures, concentrated agents on both sides, and constant mar-
ginal costs. We de ne and characterize stable market outcomes. Buyers exclusively
trade with the supplier with whom they achieve maximal bilateral joint welfare. Prices
equal marginal costs. Threats to switch suppliers set maximal fees. These also arise
from a negotiation model that extends price competition. Competition in both prices
and fees necessarily emerges. It improves welfare compared to price competition, but
consumer surpluses do not increase. The minimal infrastructure achieving maximal
aggregate welfare di¤ers from the one that protects buyers most.