本文採用Hotelling的不完全覆蓋市場空間模型，假設產品的水平異質特性由廠商內生決定，建立一個三國二廠商的三階段貿易模型，探討廠商從事Cournot數量競爭下本國政府的最適單向出口政策。本文發現當產品的異質程度內生決定時，提高出口稅會創造一個水平異質效果，透過擴大產品之水平異質程度以降低競爭，進而提高價格與利潤水準，本國政府的最適單向出口政策爲課徵出口稅。其次，本文發現若二廠商均爲區域獨占廠商(local monopolist)，則最適政策爲自由貿易。再者，本文証明若短期內產品的異質程度來不及調整，則水平異質效果消失爲0，本國政府的最適單向出口政策仍爲出口補貼。最後，我們發現若外生的水平異質程度愈高，則本國政府會對廠商提供愈高的出口補貼率。 Using an uncovered market embedded in Hotelling's linear city model, this paper constructs a three-country, two-firm trade model with a three-stage game to explore the unilateral optimal export policy under Cournot competition, when the degree of horizontal differentiation is endogenously determined. The paper shows that a rise in the export tax creates a horizontaldifferentiation effect to mitigate competition by enlarging the degree of horizontal differentiation. This leads to the result that the optimal export policy of the domestic country is to levy a tax. However the optimal policy is free trade if the two firms act as local monopolists. The optimal policy is to subsidize, if the degree of horizontal differentiation remains unchanged in the short run. Lastly, the paper shows that a rise in the degree of horizontal differentiation raises the optimal rate of subsidy.
