We use historical variation in the market share of agricultural cooperatives to examine the nature of the cooperative firm. Our data include the share of sectoral output accounted for by cooperative firms across 15 commodity sectors during the period 1930-2002. We test a simple financial contracting model where the cooperative firm is viewed as a particular implementation of "monitored credit" (or "informed intermediation"). Controlling for sectoral and year effects, we find support for the main prediction of our model with a positive and statistically significant relationship between cooperative market share and real annual lending rates.