This paper studies how intermediary’s market power changes the welfare effects of tariffs in agricultural markets. We extend the Flexible Oligopoly–Oligopsony Model (FOOM) to an open economy where processors buy from domestic and foreign farmers, combine inputs through an Armington CES aggregator, and exercise market power in both input and output markets. We calibrating the model to the U.S. beef supply chain and find three major results. Market power dominates the welfare picture, costing roughly an order of magnitude more than any plausible tariff. The textbook welfare-improving tariff disappears at empirically estimated meatpacker market power; the optimal tariff falls to zero and becomes a welfare loss beyond it. Tariff incidence shifts from foreign farmers under competition to domestic consumers under concentration. These results indicate that antitrust enforcement and trade policy are not separable interventions in concentrated agricultural markets.
