We integrate a differentiated goods oligopoly model with a political-economy model to assess the effectiveness of the partial price-ceiling policy in the Israeli fluid-milk market. We estimate minor political influence of the industry on regulators with respect to the price ceilings, and find markups in the regulated segment considerably lower than those in the unregulated one. Compared to a simulated unregulated industry, the prevailing partial price-ceiling regulation is found reducing market prices by 22% and markups by 78%, and increasing social welfare by 12%. The hypothesis of collusion in the unregulated segment is statistically rejected. We show that the combined estimates of political influence and demand substitution across products turn collusion in the laissez-faire segment an inferior strategy from the industry’s perspective.