China National Petroleum Corporation (CNPC) invested 28 million U.S. dollars last year in China's largest coal-bed methane (CBM) project in Qinshui Basin, according to a company report.

The project, located in northern China's Shanxi Province, boasts a verified reserve of 75.4 billion cubic meters.

CNPC dug 230 coal-bed gas wells in 2006 and 55 of them have been put into operation, said the report.

The gas field is located next to China's huge West-East gas pipeline, which transports gas from the western regions to the energy-hungry east.

Safety measures for the mining of CBM are notoriously lax. China has the highest number fatalities from coal mine accidents in the world and 80 percent of them are caused by gas explosions.

However, CBM is a source of clean energy. Industry experts believe it will become a practical and reliable substitute energy resource for natural gas as the global shortage of energy resources worsens and conventional natural gas supply falls short of market demand.