大部份人們在學習傳統經濟理論的過程中往往認為市場競爭程度愈激烈是促進社會福利增加的必要條件，但愈來愈多的研究顯示大規模的市場進入行為並不一定就會使得整體社會福利增加。另外在傳統研究中通常假設產品的生產都集中在一個垂直整合廠商內部解決，但是在實際生產過程中，產品的製造通常可分別有不同的製程階段，現行商業競爭環境裡上下游垂直分離的產業型態也不遑少見，因此本文設立一個上下游垂直分離產業的寡占模型，進行二階段賽局分析，並探討上下游部門廠商的市場進出條件如何影響此一垂直相關產業之廠商競爭行為、上下游部門之廠商家數、與產業利潤水準及社會福利等。
研究結果我們可以發現，當我們假設在不同的上下游市場結構條件時，確實會對於整體產業利潤、中間財價格及市場總產出等分別造成不同的變化。而在社會福利方面，當我們探討上游市場開放廠商自由進出或不開放的假設下時，只要開放下游廠商也自由進出後都將能提高整體社會福利，但當下游市場在不開放廠商自由進出的假設下時，開放上游廠商自由進出後的社會福利將分別受到下游廠商進入成本、下游廠商家數或者是上游廠商家數三者的影響。

The most people in the study tradition economic theory often thought the market competition degree is intense promotes the essential condition which the social welfare increases, but recent researchers have already discussed the implications of entry on social welfare to a large extent and found that entry does not increase welfare always. Previous works are useful the input suppliers and final good producers are vertically integrated; those analyses may not be suitable in vertically separated industries. Let us consider an economy with upstream and downstream markets, there are upstream firms producing a homogenous input and downstream firms producing homogenous goods to final consumers. We discuss the upstream and downstream department manufacturers the market turnover condition how to affect manufacturer of competition behavior this vertical correlation industry, the number of firms, industrial profit and the social welfare.
This model analysis under free entry in the upstream market supposition or not, we find that entry in the downstream market always increases social welfare. But we discussed the downstream market when does not permit the firm free entry under the supposition, after upstream firms free entry social welfare respectively will receive the downstream firm’s entry cost, the number of downstream firms or the number of upstream firms three influences.

致謝.................................................................................. I
中文摘要......................................................................... II
英文摘要........................................................................ III
目次................................................................................ IV
第一章 緒論.................................................................... 1
第一節 研究動機與目的................................................ 1
第二節 研究架構............................................................ 3
第二章 模型分析............................................................ 4
第一節 上下游市場不允許廠商自由進出之均衡........ 4
第二節 上游市場允許廠商自由進出之均衡................ 9
第三節 下游市場允許廠商自由進出之均衡.............. 13
第四節 上下游市場允許廠商自由進出之均衡.......... 16
第三章 市場進入與社會福利...................................... 18
第一節 上游市場允許進出下的社會福利分析.......... 19
第二節 上游市場不允許進出下的社會福利分析...... 20
第三節 上游市場允許進出下的社會福利分析.......... 21
第四節 下游市場不允許進出下的社會福利分析...... 22
第四章 結論.................................................................. 24
參考文獻....................................................................... 26

Abiru M., B. Nahata S. R. and M. Waterson (1998), “Equilibrium Structures in Vertical Oligopoly," Journal of Economic Behavior & Organization, 37, 463-480.
Greenhut, M. L. and H. Ohta (1979), “Vertical Integration of Successive Oligopolists,” American Economic Review, 69, 137-141.
Higgins, R. S. (1999), “Competitive Vertical Foreclosure,” Managerial and Decision Economics, 20(4), 229-37.
Horn, H., Wolinsky, A., (1988), “Bilateral monopolies and incentives for merger,” Rand Journal of Economics, 19, 408–419.
Lin, Y. J. (1988), “Oligopoly and Vertical Integration: Note,” American Economic Review, 78 (1),251-54.
Mankiw, A. G. and M. D. Wihinston, (1986), “Free entry and social inefficiency,” Rand Journal of Economics, 17, 48 – 58.
Matsushima, N.,(2006), “Industry profits and free entry in input markets,” Economics Letters, 93, 329-336.
Naylor, R.,(2002), “Industry profits and competition under bilateral oligopoly,” Economics Letters, 77, 169-175.
Salinger (1988) “Vertical Mergers and Market Foreclosure,” Quarterly Journal of Economics, 103, 345-356.
Schmalensee, R., (1976), “Is more competition necessarily good, ” Industrial Organisation Review, 4: 120 – 21.
Schrader, A. and S. Martin (1998), “Vertical Market Participation,” Review of Industrial Organization, 13, 321-331.
Spence, M., (1984), “Cost reduction, competition, and industry performance,” Econometrica, 52, 101 – 21.
Stiglitz, J. E., (1981), “Potential competition may reduce welfare,” The American Review, 71, 184 – 89.
Suzumura, K. and K. Kiyono, (1987), “Entry barriers and economic welfare,” The Review of Economic Studies, 54, 157 – 67.
Tandon, P., (1984), “Innovation, market structure, and welfare,” The American Economic Review, 74, 394 – 403.
Tyagi, R. K., (1999), “On the effects of downstream entry,” Management Science, 45,59 – 73.
von Weizsäcker, C. C., (1980a), “A welfare analysis of barriers to entry,” Bell Journal of Economics, 11, 399 – 420.