Beijing's investigation of China National Petroleum Corp executives exposes the country's largest state-owned energy firm to possible probes by the authorities in the United States and Britain under their anti-bribery laws, analysts said.
The investigation is believed to be linked to former security tsar Zhou Yongkang.
Beijing has opened an investigation into Zhou, an ally of fallen official Bo Xilai, which will include Zhou's activities at CNPC.
Four executives of the company - Li Hualin, Ran Xinquan, Wang Daofu and Wang Yongchun - are being investigated for breaches of discipline.
CNPC's subsidiary, PetroChina, is listed in New York, rendering both companies vulnerable to investigation by the Department of Justice and the Securi- ties and Exchange Commission, said Keith Williamson, the head of forensic and dispute services in Hong Kong and mainland China at Alvarez & Marsal, an international professional services firm.
"With cases of alleged corruption that involve companies which have some connection to the US, I expect the US authorities to make an initial assessment of whether the alleged corrupt activity involves entities incorporated or listed in the US," Williamson said.
Daniel Roules, a partner at US law firm Squire Sanders, said the Department of Justice would not be seeking to cause an international incident over its investigation, but the governments of both countries wanted to root out corruption.
So it would want to co-operate with the Chinese authorities if possible, Roules said. "Even if there is no collaboration, the DOJ will not be deterred simply because people in China do not want DOJ to be involved."
If the department decides not to investigate CNPC under the Foreign Corrupt Practices Act, it could use anti-money laundering laws to investigate, Roules said.
Even if the bribes were paid in China, if the recipient deposited the money in a US bank or cleared it through a US bank, it would be a sufficient connection for an investigation, he said.
David Lee, a partner at Norton Rose Fulbright, said there had been several instances of international co-operation with US authorities on anti-corruption issues.
In May, French energy giant Total paid the US government US$398 million in fines to settle bribery charges in Iran.
PetroChina, which is also listed in Hong Kong and Shanghai, has British subsidiaries, making it and CNPC subject to the Bribery Act, Lee said.
A PetroChina spokesman said the company "will disclose relevant information in a timely matter in accordance with regulatory requirements".