BEIJING - China National Petroleum Corporation (CNPC) announced on Tuesday that it has discovered a major "tight oil deposit" in Northwest China's Shaanxi province.

Tight oil is an unconventional energy, which exits in petroleum-bearing formations like shale or sandstone. Commercial production usually requires similar technology to shale gas production.

The CNPC estimated the reserve in the deposit is around 100 million tons, the largest one ever discovered in China, and will produce 700,000 tons of tight oil annually.

China is one of the world's largest oil buyers, and nearly 60 percent of its oil consumption comes from imports.

To keep external dependence under 61 percent, the government is assessing solar and wind power as well as unconventional energy including shale gas and tight oil.