本文探討國際海運在貿易政策中的角色，分析上游海運商定價策略如何影響一國政府之最適政策與社會福利。本文建立一個兩國相互貿易模型，假設兩國下游廠商在本國與外國市場進行 Cournot 數量競爭，且兩國出口須使用註冊在本國的海運商所提供之運輸服務。本文的研究結果顯示，在完全競爭海運市場下，海運商無法取得超額利潤，兩國政府之最適進口政策呈現對稱，都會對進口商品課徵關稅。但是，當海運商具有市場力量時，本文發現當海運商採取差別運輸費率定價下，外國政府會提高關稅稅率，本國政府卻會降低關稅稅率。特別值得一提的是，本文發現當海運成本與產品替代程度較低時，本國政府的最適進口政策甚至會是進口補貼。另一方面，當海運商統一收取運輸費率下，本研究也顯示本國(外國)政府會對進口商品課徵比在完全競爭海運市場狀況為低(高)的關稅稅率。整體而言，本文指出海運商的市場力量的確會影響進口國家貿易政策的制定方向。

This paper examines the role of international maritime shipping in trade policy by analyzing how upstream shipping pricing regimes affect governments' optimal policies and social welfare.We develop a two-country reciprocal trade model in which downstream firms in both countries engage in Cournot quantity competition in domestic and foreign markets. Cross-border exports must use transportation services provided by a shipping firm registered in the home country.
The results show that when the maritime shipping market is perfectly competitive, the shipping firm cannot earn excess profits, and the optimal import policies of the two countries are symmetric, with both governments imposing tariffs on imported goods. However, when the shipping firm has market power, policy outcomes become asymmetric. Under discriminatory freight pricing, the foreign government raises its tariff rate, whereas the home government lowers its tariff rate. In particular, when maritime shipping costs and product substitutability are relatively low, the home government's optimal import policy may even become an import subsidy.
In contrast, when the shipping firm adopts uniform freight pricing, the home government imposes a lower tariff than under perfect competition in the shipping market. In comparison, the foreign government imposes a higher tariff. Overall, this paper demonstrates that shipping firms' market power plays an important role in shaping the direction of trade policy in importing countries.

論文審定書.............................................................................................................i
摘要....................................................................................................................ii
Abstract.............................................................................................................iii
目錄...................................................................................................................iv
圖次...................................................................................................................vi
第一章　前言....................................................................................................1
第二章　基本模型設定
2.1　市場結構與需求函數...............................................................................5
2.2　政府政策與海運服務定價......................................................................6
2.3　下游製造廠商..........................................................................................6
2.4　消費者剩餘與社會福利..........................................................................7
2.5　雙邊貿易..................................................................................................7
2.6　賽局時序與小結.......................................................................................8
第三章　完全競爭海運市場下的均衡分析
3.1　下游市場均衡...........................................................................................9
3.2　完全競爭下的消費者剩餘、廠商利潤與社會福利..............................9
3.3　完全競爭下的最適政策........................................................................10
第四章　差別取價下的均衡分析
4.1　下游市場均衡.........................................................................................13
4.2　海運商差別取價.....................................................................................13
4.3　差別取價下的均衡產量........................................................................14
4.4　差別取價下的廠商利潤、上游海運商利潤、消費者剩餘與社會福利..........................................................................................................................14
4.5　差別取價下的最適關稅稅率................................................................16
第五章　統一定價下的均衡分析
5.1　下游市場均衡.........................................................................................19
5.2　海運商統一定價.....................................................................................19
5.3　統一定價下的均衡產量........................................................................20
5.4　統一定價下的廠商利潤、消費者剩餘與社會福利............................20
5.5　統一定價下的最適政策........................................................................22
第六章　差別取價、統一定價與完全競爭之比較
6.1　三種制度下政府最適政策之比較........................................................25
6.2　差別取價下的補貼誘因........................................................................26
6.3　補貼的出現時機.....................................................................................26
6.4　海運成本對政策影響方向之影響........................................................27
第七章　結論..................................................................................................29
參考文獻..........................................................................................................30

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