China constructed two new oil and gas platforms in the East China Sea in May and June, drawing formal protests from Japan. But in addition to these new permanent structures, satellite imagery and automatic identification system (AIS) data shows that at least three mobile drilling rigs have also been active in the area, supporting both production and exploration activities—and potentially laying the groundwork for the construction of more permanent platforms in the future.
The new structures bring the total number of Chinese fixed platforms near the median line between China and Japan to twenty. Tokyo has long protested Beijing’s oil and gas development in the area, arguing that China is tapping into hydrocarbon reserves that straddle the line and should therefore be shared between the two countries. Beijing and Tokyo agreed to establish a joint development zone in the area in 2008 in part to address this concern, but between 2013 and 2015 China built a dozen platforms along the median line just south of the zone. Under Japan’s domestic law, Tokyo treats the median line as a de facto boundary in the absence of a delimitation of the two countries’ overlapping continental shelf claims. Beijing does not formally recognize the median line but has thus far been careful to keep its development activities on the Chinese side.
Installation of the new platforms 15 and 16 was conducted by the 300-meter crane ship Zhenhua 30.
The crane ship Zhenhua 30 and heavy-lift ship Debo 3 installing platform 15 on May 13, 2025.
Satellite imagery and automatic identification system (AIS) tracking data show the Zhenhua 30 at work installing platform 15 from May 10 to 24, then returning to Ningbo-Zhoushan port before heading back and installing platform 16 from June 18 to 30. The Zhenhua 30 then headed south along China’s coast toward Guangdong province where it has remained since early July, suggesting that construction near the median line has ended for now.
China last installed a new permanent structure in the area in 2022. In the three years since, AIS data shows that at least three Chinese mobile drilling rigs—Oriental Discovery, Shanghai Zhenhua, and the Nan Hai 10—have been active in the area.
As in years past, the mobile rigs on several occasions linked up with fixed platforms, likely to increase production through infill drilling or recompletion of existing wells. But perhaps more interestingly, the drilling rigs were also seen operating for months at a time from at least 12 locations with no existing production facilities. Depending on the results of the exploratory drilling at these sites, they could be targets for future construction of production platforms. Given China’s consistently assertive approach to maritime resource exploitation, it is almost certain that the latest two fixed platforms will not be the last.
