CLARK FIELD, PHILIPPINES - A standoff between Chinese and Vietnamese vessels in the South China Sea has intensified with the return this month of China's oil survey boat - followed by a reprimand from U.S. natural security adviser John Bolton.

While Sino-Vietnamese spats regarding the disputed sea have surfaced regularly since the 1970s, this one is lasting longer and with little of the problem-solving diplomacy that often follows an upset. The standoff began in June when a Chinese energy survey ship, the Haiyang Dizhi 8, began patrolling waters near Vanguard Bank, 352 kilometers off the coast of southeastern Vietnam. Vietnam operates an undersea energy exploration platform near Vanguard Bank.

China and Vietnam both claim western parts of the 3.5 million-square-kilometer sea. China is militarily and economically stronger than Vietnam.

Here are three scenarios for an outcome to the Vanguard Bank standoffs:

More players, more escalation

China's vessel may stay near Vanguard Bank or get backup, especially if foreign governments level too much criticism on Beijing.

"China's recent escalation of efforts to intimidate others out of developing resources in the South China Sea is disturbing," Bolton tweeted on Tuesday. "The United States stands firmly with those who oppose coercive behavior and bullying tactics which threaten regional peace and security."

Australian media reports say two days later, Australia's prime minister, speaking in Hanoi, said Chinese neighbors should resist "coercion."

Dangers of tough messaging

Messages such as these, if they get any tougher, could drive China to increase its show of strength toward Vietnam, said Yun Sun, East Asia Program senior associate at the Stimson Center research group in Washington.

China says the decades-old maritime dispute, the biggest in Asia, should be settled among the Asian claimants rather than outside countries. Brunei, Malaysia, the Philippines and Taiwan also claim parts of the same resource-rich contested sea. To keep up relations, China is helping some of the claimants economically.

The U.S. government regularly sends naval vessels into the sea to check China's expansion.

"If that is indeed the plan (for the U.S. government) to support Vietnam's position, I don't think the Chinese will stand aside," Sun said. "I think it will escalate."

Stormy weather

South China Sea claimants have cited weather before in quitting standoffs with other countries. In June 2012, Philippine leaders cited stormy weather as a reason for withdrawing two coast guard ships from a shoal disputed by China.

"Weather is always a good excuse," said Oh Ei Sun, senior fellow with the Singapore Institute of International Affairs.

Other events may give China a convenient reason to retreat, too. The Chinese oil survey vessel had left Vanguard Bank by early August as top Chinese leaders met near Beijing for an annual conference. The vessel returned after leaders had hashed over foreign policy this year, Sun said.

Party-to-party negotiations

The two countries periodically ease disputes through meetings between envoys from the ruling communist party of each side. Those informal encounters often build enough goodwill to allow calm after an incident, yet without a formal resolution that would require tougher talks between officials.

"The old tried and true third scenario is that party-to-party ties would see an envoy go," said Carl Thayer, emeritus professor of politics at The University of New South Wales in Australia. To this end, he said, "Vietnam has repeatedly made full court press on every possible channel."

The two sides normally wait until an incident has lasted a week or two before one proposes party-level talks, Oh said. Then the party representatives would usually resolve the issue within another month, he said.

"I think at some point there will be some sort of face saving for both sides after the party channels are activated," Oh said.