The National Audit Office has begun to audit four state enterprises, including China National Petroleum Corp, and the Ministry of Railways.
China Huadian Corp, Harbin Power Plant Equipment Corp and China Resources are also being audited.
Deputy Auditor-General Yu Xiaoming said CNPC would be audited in four main areas: accuracy of its internal audit, procedures for key decision-making, business operations considered irregular and management of state assets.
For the Ministry of Railways, auditors would review major construction projects and the financial status of 17 railways bureaus and three companies under the ministry's management. Xinhua said the railways' audit was the most extensive since 1998.
A CNPC official confirmed the audit had started, but stressed the company had nothing to fear. 'Everything is perfectly fine here. We don't have anything that is not open to audit,' he said. He insisted CNPC was chosen not because the company had a problem, but because it was a big company.
Auditor-General Li Jinhua said earlier that audits of state-owned industry monopolies were key to maintaining the country's financial stability.
The National Audit Office also released the results of its audit of 34 road schemes and found 2.16 billion yuan was misused or embezzled, and 3.25 billion yuan was wasted.
The audits found 15 projects had occupied more than 40,000 hectares of land beyond approved limits.