The country's two major oil providers China National Petroleum Corp and China Petroleum and Chemical Corp have been punished by the Environmental Protection Ministry for failing their 2012 environmental tests.

The evaluation, released on Aug 29, was based on four indicators: chemical oxygen demand, which shows the concentration of organic matter in the water; ammonia nitrogen, a major cause of excessive nutrients in water; and the airborne pollutants sulfur dioxide and nitrogen oxide.

The indicator for chemical oxygen demand for China National Petroleum Corp, or CNPC, Asia's largest oil and gas producer, was reduced by 0.08 percent in 2012, far below the target reduction of 0.6 percent.