This paper examines the theoretical specification of structure-performance hypotheses in a value-maximizing model of oligopoly decision-making under risk. Price-cost margin, advertising intensity, and non-diversifiable risk are related to the elements of market structure, cost fixity, output variance, advertising cost, brand introductions, leverage, asset size, and the correlation between firm and market returns. The roles of two previously omitted variables--market price elasticity and BETA--emerge from the theoretical analysis and are confirmed by the empirical results.