PetroChina is one of the country's biggest state-owned companies
Chinese authorities are investigating three senior executives of state-owned energy firm PetroChina over "serious breaches of discipline".
China's State-Owned Assets Supervision and Administration Commission, which oversees state firms, did not provide details of the breaches.
PetroChina said two vice-presidents and its chief geologist resigned on Tuesday because of "personal reasons".
The firm's shares fell as much as 5% in early trade in Hong Kong.
PetroChina said in a statement that Vice Presidents Li Hualin and Ran Xinquan as well as Chief Geologist Mr Wang Daofu "are currently under investigation by relevant People's Republic of China authorities".
It added that the three officials had resigned from the their respective positions "with immediate effect".
China has upped its efforts to tackle corruption in the country.
Last week, disgraced Chinese politician Bo Xilai was put on trial on charges of corruption, bribery and abuse of power.
China's President Xi Jinping has said corruption is a threat to the survival of the ruling Communist party and has urged authorities to take steps to tackle the problem.
Source: BBC News - Business http://www.bbc.co.uk/news/business-23860206#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
