Tensions in Sino-Japanese relations were escalating once again this month.

On July 15 Cui Tiankai, director of the Foreign Ministry's Asian Affairs Department, summoned Chihiro Atsumi, minister in charge of the Japanese embassy's economic section in China, to lodge a solemn complaint against Tokyo's decision to give a private Japanese oil company gas and oil drilling rights for areas east of the "median line" in the East China Sea.

The so-called "median line" was unilaterally demarcated by the Japanese government and has never been accepted by the Chinese side.

The East China Sea lies between the Chinese mainland and the Japanese Ryukyu Islands, with its northern part abutting the Korean Peninsula.

Its widest breadth between east and west is 360 nautical miles and only 167 nautical miles between the two nearest points.

According to the 1982 UN Convention on the Law of the Sea, all coastal states can claim an exclusive economic zone (EEZ) within 200 nautical miles of its baseline from where its territorial sea is measured.

But the average width of the East China Sea between China and Japan is only a little more than 210 nautical miles.

That means the two nations' EEZ claims overlap and thus must be divided through consultation.

The two countries began to discuss maritime jurisdiction division from 1996 when China became a member of the UN Convention on the Law of the Sea. The legal document, also signed and ratified by Tokyo, has provided legal references for bilateral consultations.

However, due to the huge differences between the two countries over maritime border demarcation, no fundamental progress has been achieved after rounds of talks, except a fishery accord signed in June 2000.

The biggest obstacle to reaching a consensus is the different approaches of the countries to the talks, according to a Chinese Foreign Ministry official who once took part in negotiations.

China proposes equitable principles be adopted, while Japan insists the "median line" be taken.

Japan's so-called "median line" runs between its northern islets and the Diaoyu Islands, which belongs to China but is claimed by Japan, and China's coastal islands.

If this line is adopted, the area of sea under Japanese control would be 160,000 square kilometers larger than it should be in the spirit of the principle of "natural extension of the continental shelf," as stated in the 1982 UN Convention.

It is an international practice that small, uninhabited islands that are disputed should not be used as baselines for sea border demarcation, Gao Jianjun, a maritime law expert at the China University of Politics and Law, pointed out.

Experts said they believe that by putting forward the "equidistant median line" principle, the Japanese government has demonstrated its explicit intention to include the Diaoyu Islands on its territorial map and expand its maritime territory into Chinese waters.

Last summer, China began to operate natural gas projects in its EEZ in the East China Sea. But this legal move has provoked radical reactions in Japan.

Although China has never accepted the "median line," unilaterally drawn by Japan, it has not extended its gas drilling activities beyond the line, to avoid friction with its neighbor.

Japanese media claim such projects are not in Japan's national interests. The Japanese government sent vessels to disputed waters to investigate while refusing China's proposal of "shelving disputes for joint development."

Tokyo has also demanded on many occasions that China stop "unilateral" drilling activities. It claimed China's gas field straddles the "median line."

After Japan failed to obtain gas field data, which is absolutely secret, it resorted to claiming China's drilling would inevitably siphon off gas from its reserves.

Such an assertion shows Japan's obvious lack of scientific understanding of the structure of gas fields, according to oil experts.

To extract natural gas from Japan's claimed side of the "median line" would require completely separate drilling.

In reaction to China's refusal to provide data, the Japanese government approved test drilling by a private oil corporation in the disputed area of the East China Sea.

The move was an attempt to cause a de facto recognition of the "median line" between the two countries, analysts said.

According to the Japanese media, Tokyo has appropriated billions of yen to assist such test drilling activities.

If Japan insists on unilateral gas exploration in the disputed area, the East China Sea will inevitably become "waters of confrontation," said Yu Mincai, an associate professor of law at Renmin University of China.

China would have no choice but to intervene then, Yu said in an article on the Nanfang Weekend newspaper.

In view of the huge differences in maritime demarcation, the two countries should adopt universally accepted international principles as soon as possible to solve the dispute in the East China Sea.

According to Zhang Aining, an associate professor of international law at the Beijing-based Foreign Affairs College, there are two laws to be referred to involving the sea area division between neighboring countries. One is the Geneva Convention of the Continental Shelf signed in 1958 and the other is the 1982 UN Convention on the Law of the Sea.

Japan's principle of an "equidistant median line" was put forward in accordance with the sixth article of the former document. The problem is that only signatories are bound to abide by an international treaty. China and Japan have so far not signed the convention.

The settlement of similar disputes around the world shows the principle has not become an international practice that is universally accepted.

Thus the latter document, which has been signed by more than 140 states, including China and Japan, should provide the main legal reference for the two neighbors to solve their disputes, according to experts.

The convention puts forward the principle of "demarcation through consultations" and rules out unilateral delimitation.

According to the document, the continental shelf of a coastal state comprises the seabed and subsoil of the submarine areas that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a distance of up to 200 nautical miles from the baselines from which the breadth of the territorial sea is measured.

However, there has been a dispute between China and Japan about the legal status of the Okinawa oceanic trough.

China claims the trough, 2,700 meters deep, can be regarded as the point that divides the continental shelf with Japan. At the same time, China also agrees to take other factors into consideration in the division.

However, Tokyo refuses to recognize this.

So given their different stances, only consultation is in the interests of both countries.

(China Daily July 28, 2005)