An analytical model to evaluate the effectiveness of u.s. generic milk advertising which incorporates the degree of market competition is presented. Unlike traditional perfect competition models, the imperfect competition model allows for simultaneous movement of both price and quantity with an endogenous fluid (Class I) price differential. The simulation results of the imperfect competition model are compared with the conventional exogenous fluid price differential model. It is shown that the conventional fixed fluid price differential model may under-state the effectiveness of U.s. generic milk advertising in terms of returns to producers.