併購與分割同樣屬於公司層級的策略，併購的策略一向被媒體大眾所關注，不但併購案數量較多，而且相關的研究文獻也較多，分割策略相對的就沒那麼受到注目。過去的學者對於分割的研究多著重在個案的探討和異常報酬的發生，以單一產業內的分割公司經營效率的研究尚未有人進行探討。本研究試圖進行探索式研究，以石油與天然氣產業為研究對象，欲了解在同樣的產業下有分割的公司是否經營效率比未進行分割的公司更為優異。 在石油與天然氣產業裡，由於產業特性的關係，多是國際企業或是國營企業，這些公司規模龐大有進行分割的誘因。在本研究中最終觀察的樣本有分割公司8間，未分割公司56間。研究方法選用動態資料包絡分析法。實證結果顯示有分割過的公司在效率的表現上相對較差，有可能是因為經營不佳才希望透過分割的策略改善公司的經營效率，分割之後所帶來的效率提升會隨時間減少。此外在不同景氣下，景氣好的時候有分割的公司經營效率較佳，景氣差的時候則較差，因石油與天然氣產業屬於受景氣循環的產業，故這樣的現象可以視作是產業聚焦所造成的結果。 ;M & A strategy and spin-off strategy also belonging to the company-level strategy, mergers and acquisitions strategy has always been of concern to the public media, not only the large number of mergers and acquisitions, but also more relevant research literature, spin-off strategies are not so opposed to the limelight. Past scholars study focuses on case studies and cumulative average abnormal return. Spin-off operating efficiency studies to explore yet someone within an industry. This study attempts to conduct exploratory research to the oil and gas industry as the research object, I want to know in the same industry have spun off over whether the company is not operating efficiently spin off the company more excellent. In the oil and gas industry, due to(because of) the characteristics of the industry, mostly having international companies or state-owned enterprises. It is attractive for the large-scale company to spin off. In this research, the final samples are 8 spin-off companies and 56 companies which is not spin-off. Research method is data envelopment analysis. The empirical results show the spin-off company′s relatively poor performance in terms of efficiency. The result might be because the motivation for the companies to take spin-off strategy is trying to improve the poor management efficiency, and the gain of efficiency by taking the spin-off will reduce over time. Furthermore, it has different situation in the different business cycle. When the business cycle is prosperous, the spin-off companies have better operating efficiency. Otherwise, it have poorer efficiency in the economic depression. Oil and gas industry are subject to cyclical industries, the industry can be explained as the result of this focus.