The share of patronage refunds retained by an agricultural cooperative is modeled as arising from the portfolio decision of its median member. The member is viewed as maximizing expected utility by allocating wealth between investments in farming assets and equity in the cooperative. Determinants of the share of patronage refunds retained are the expected rates of return on these two investments, their variances, their covariance, and the expected future share of patronage and its variance. Empirical examinations of aggregate cooperative data and cross-section analysis of seventeen regional supply cooperatives are found to be consistent with the model.