Between 2010 and 2012, a CNPC's subsidiary invested 2.24 billion yuan in a coal-fired power plant project which failed to get government approval before construction.

CNPC, also known as PetroChina, also built a 2.1 billion yuan gas storage project in northeast China's Liaohe Oilfield in 2011 without approval. The company later got permission for the same in November 2013.

In Sichuan, PetroChina formed a joint venture to develop natural gas in December 2007 and failed to start commercial production as promised in 2009.

CNPC has been facing a series of investigations since last year after the central government decided to crackdown on corruption. Jiang Jiemin, former CNPC chairman and at least six other high-ranking officials are being investigated for corruption-related charges.

According to the NAO, about 190 people at 11 State-owned enterprises have been punished for policy breaches or mismanagement during the auditing survey.

China Resources' affiliates purchased vehicles at numbers and prices far beyond the stipulated limits, said the office. Song Lin, former China Resources chairman was investigated for "suspected disciplinary violations," in April.

A senior auditor with one of the big four audit firms, who declined to be named, said the report shows that CNPC lacks internal management and strict supervision of its subsidiaries.

"To prevent such things from happening, the company needs to strengthen its internal controls," he said. "The national auditor should also audit the firm in a timely manner."

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