The judiciary has relied on a firm's market share to evaluate the presence of monopoly power for a Sherman Act monopolization violation. However, an allegation that a firm's market share constitutes monopoly power may be refuted by evidence that there exists a contestable market. Contestable market theory shows that there is no monopoly power where there exists a threat of entry of other firms. This theory thereby offers agricultural cooperatives, which may have a large market share by reasons of the antitrust immunity provided by the Capper-Volstead Act, an argument to overcome allegations of a Sherman Act monopolization violation.