The move would help improve air quality, an environmental official said.

The revised lead-free gas standard, to be announced by the end of this year, will drive gas with sulfur levels of 500 ppm out of market on Dec. 31, 2009, said Li Xinmin, deputy director of the pollution control department of the State Environmental Protection Administration (SEPA), at a symposium on automobile pollution control.

The new standard would meet the Euro-III emission norm, which constrained sulfur levels to 150 ppm maximum.

"Automobile emissions have become a major factor of urban pollution, " Li said.

Statistics from the SEPA show China produced almost 6.21 million cars in the first ten months this year and it is expected the country's automobile output will exceed seven million for the whole year.

In the first half, sulfur dioxide emissions increased by 4.2 percent, from the same period a year earlier.

Sinopec, the China Petroleum and Chemical Corporation, one of the major petroleum companies in China, announced plans to invest 30 billion yuan (3.75 billion U.S. dollars) in reducing the sulfur levels in gasoline.

Xu Hui, deputy director of Sinopec's technology development department, said some companies were already capable of producing gas with sulfur levels less than 150 ppm.

It would take a lot of effort to meet the new gas standard, Li Xinming said, adding that currently only gas provided in Beijing and Guangzhou contain low levels of sulfur.

Xu said gas producers would find it difficult to reduce sulfur levels as the sulfur levels in imported crude oil were high: an average of 1.11 percent of the imported oil by Sinopec in the first ten months, whereas sulfur levels of imported oil in 1999 was only 0.17 percent.

The high sulfur level of crude oil would pose a challenge to making clean auto fuel, Xu said.

China banned the sale of gasoline containing lead in July 2000.Experts estimate the move reduced lead emissions by 1,500 tons each year.