Workers seen walking inside China National Petroleum Corporation (CNPC) Lanzhou Chemical Company in Gansu province in this April 27, 2007 file photo. [Reuters]

China's top oil companies plan to boost the supply of cleaner fuels such as natural gas to Beijing to help clear the capital's smoggy skies in the run-up to next summer's Olympic Games, industry media reported on Tuesday.

China National Petroleum Corp. (CNPC), China's biggest oil and gas producer, plans to increase Beijing's natural gas supply by 17 percent to 5.5 billion cubic metres in 2008, the China Petroleum Daily reported.

The increased supplies will help to replace coal used in water heaters and electric power plants and will substitute for coal gas in cookers. It will also power some buses and cabs in the city, said the newspaper.

Sinopec, China's largest refiner, has also upgraded its Beijing plant to produce cleaner fuels, the China Petrochemical News reported.

The Yanshan plant, with 10 million tonnes of crude processing capacity, is fully ready to produce gasoline and diesel to meet the Euro IV low-sulphur standard, after 5.7 billion yuan ($750 million) in new investments, the newspaper said.

Beijing will lead the country in adopting the Euro IV standard in 2008, which limits sulphur levels in gasoline to no more than 50 parts per million.