Little progress has been made in testing the often conflicting hypotheses generated from theoretical research on cooperatives. This paper addresses the deficiency by describing and applying (to California cotton ginning cooperatives) a methodology to test key hypotheses concerning (a) cooperatives’ price-output equilibrium, (b) allocative efficiency, and (c) utilization of capital inputs. The empirical results (a) are consistent with predictions from the game theory model of cooperative behavior, (b) reject the null hypothesis of absolute allocative efficiency, and (c) indicate absolute overutilization of capital inputs among the sample cooperatives.