本文以 Victor D. Cha 之日韓準同盟理論分析，探討日、韓雙方在東海油氣田爭端上不斷出現合作與衝突局面擺盪的特性。由過去日、韓雙方在東海油氣田爭端上之互動，可以看出以下的特性:(1)在雙邊關係上，當日韓兩國所面對的「拋棄」或「牽連」的不安感程度為「不對稱」時，如 1972 年 美國總統尼克森訪問中國之後，日、韓之間因此而產生衝突，並促使日韓各自試圖與中國合作;(2)當日韓兩國面對的「拋棄」或「牽連」的不安感程度為「對稱」時，如 1977 年美國總統卡特提出駐韓美軍全面撤離的計畫之後，兩國之間於是產生合作的關係，並減少與中國合作的動力，乃使 1978 年 6 月 22 日《韓日大陸礁層共同開發協定》正式生效;(3)兩韓關係穩定，如 2000 年 6 月南北韓首腦會談後，打造了日韓在東海油氣田上合作的 機會;(4)中國若企圖破壞日本劃定的「日中中間線」，會促使日本以「韓日共同開發區域」的名義來拉攏韓國並進行低層次的合作，以加強「日中中 間線」的立場，如日、韓對於「韓日共同開發區域」探勘資料進行共同研究之事即為一例;(5)日本若過度忽略《韓日大陸礁層共同開發協定》傷害韓國利益，會促使韓國採取因應對策，來對付日本所主張的「中間線原則」，「2012 年大陸礁層劃界申請案」即為一例。若日韓雙方能在「韓日共同開發區域」深化實際性的合作，必將提高透過共同開發協定解決東海油氣田爭端之可能性。

This research analyzed the characteristics of repeated cooperation and conflicts between Japan and Korean over disputes of the East China Sea oil and gas field based on the Japan-Korea quasi-alliance model of Victor D. Cha. In previous disputes over the East China Sea oil and gas fields, the characteristics of Japan-Korea interaction are organized as follows:

(1)When the instability level of abandonment or entrapment faced by Japan and Korea in their bilateral relationship is asymmetric, conflict arises between Korea and Japan, and each of them tries to cooperate with China separately. An example was the case after the Nixon visit in 1972;(2)When the instability level of abandonment or entrapment faced by Japan and Korea in their bilateral relationship is symmetric, Japan and Korea forms a cooperative relationship, and the drive to cooperate with China decreases. One example was the official enactment of the Korea-Japan Agreement on Joint Continental Shelf Development on June 22, 1978, after President Carter proposed a plan to withdraw US forces in Korea;(3)After the June North- South Korean meeting in 2000, the inter-Korean relationship was stabilized, opening an opportunity for Japan and Korea to cooperate on the issue of East China Sea oil and gas field;(4)When China tries to incapacitate the Japan- China median line drawn by Japan, Japan involves Korea in the name of exploration data research, Korea-Japan Joint Development Zone(JDZ), to utilize a low-level Japan-Korea cooperation. By doing so, Japan solidified its stance on the Japan-China median line;(5)If Japan acts too passively in implementing the Korea-Japan Agreement on Join Continental Shelf Development and damages Korea’s national interests, Korea actively refutes Japan’s median line principle. A main supporting case was the Korean submission of formal report to the CLCS in 2012;(6)After the rise of China, a change in the East China Sea situation is all the more desired. However, as the US pursues a pivot to Asia, more difficulties are expected in Japan-Korea cooperation in the East China Sea oil and gas fields.