PetroChina Co., the nation¡¯s largest oil and gas producer, plans to more than triple its annual natural gas output from the Sulige field in northern China in six years as demand for the cleaner-burning fuel rises.

PetroChina targets 35 billion cubic meters of annual gas production from Sulige in Inner Mongolia by 2015, parent China National Petroleum Corp. said in a statement on the government Web site Thursday. The field¡¯

s output may rise to 10 billion cubic meters this year, China National said in 2007.

China wants cleaner-burning fuels such as natural gas to be used increasingly as an alternative to coal to curb pollution and reliance on oil imports. The nation¡¯s natural gas consumption rose 16 percent last year, BP Plc said in its 2009 Statistical Review of World Energy.

The daily gas output at Sulige reached 25.58 million cubic meters on June 25, compared with 15 million cubic meters in July last year, China National said in the statement Thursday.