China's claimed territorial limits and Vietnam offshore gas fields

China claims a chunk of the Nam Con Son Basin about 370 kilometers off Vietnam's southeast coast, as set out here:

Just when it seemed China and Vietnam had buried their conflicting claims to the Spratly Islands, Beijing is contesting a new Hanoi-tendered, BP-led, US$2 billion natural-gas project near the rocky group of islands and reefs in the South China Sea. The flare-up marks perhaps the strongest indication yet that Beijing's soft-power overtures toward Southeast Asia are hardening when it comes to energy-security concerns.
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The contested Moc Tinh and Hai Thach gas fields, in the Nam Con Son Basin about 370 kilometers off Vietnam's southeast coast, are both run by British energy giant BP through a production-sharing contract with state-owned PetroVietnam and in partnership with US oil firm ConocoPhillips.

The Chinese Foreign Ministry on April 12 claimed that the project encroached on its territory, saying "any unilateral action taken by any other country in these waters constitutes infringement into China's sovereignty, territorial rights and jurisdiction. We are firmly opposed to this." Hanoi has countered that the multinational-led project lies in its territorial waters and exclusive economic area, consistent with the 1982 United Nations Convention on the Law of the Sea.

Operations map from here.

BP operations described here. Click on images to make them bigger.