CNPC, China's biggest oil producer, is the parent company of PetroChina . The firm could not immediately be reached for comment.
The graft watchdog said last month it had targeted 26 giant state-owned firms for inspections this year, including CNPC, the China National Offshore Oil., and the China National Nuclear.
Read MoreChina and Middle East will drive oil demand: OPEC
Several senior CNPC executives have already been put under investigation in a far-reaching corruption crackdown, among them former chairman Jiang Jiemin and the company's vice president, Wang Yongchun.
CCDI said on Sunday it had also put Xu Jianyi, the chairman of one of the country's top state-owned automakers, the China FAW Group Corp, under investigation for "violating Party discipline".
After taking over as party and military chief in late 2012, President Xi Jinping declared war on corruption at all levels. Scores of senior officials have been brought down by the campaign, including former security tsar Zhou Yongkang.