East China Sea, together with the Yellow Sea and the South China Sea, is one of the three half-closed water basins, separating continental China from the Pacific Ocean. It is separated from the Pacific Ocean by the Ryukyu Archipelago; the Strait of Taiwan separates it from the South China Sea. To the north, it joins with the Yellow Sea, and through the Korean Strait, with the Sea of Japan. At its shores lie the three provinces of continental China: Fujian, Zhejiang and Jiangsu. For many centuries it has been an important fishing area for its coastal countries, and is still important in terms of food security.

Between 1969 and 1970, rich oil and gas deposits of the East China Sea became a subject of interests of the countries lying at its shores. The claims were staked out by Japan, Okinawa (at that time being under the US administration), South Korea, and Taiwan. The unilateral claims were based on the Convention on the Continental Shelf, signed in Geneva in 1958, and they referred to 11 seabed petroleum blocks altogether. The four Japanese blocks and Okinawa's block were claimed by private oil interests, unlike South Korea's two and Taiwan's four which were claimed by the respective governments. Unilateral claims of Japan were supported by the so-called median principle, while Korea and Taiwan based on the natural prolongation of the shoreline principle. Inevitably, the claims overlapped one another to different extents.