SHANGHAI, Oct 11, 2007 (AFP) - PetroChina, China's largest oil and gas company, has discovered a major gasfield in the nation's northwest Xinjiang region, state media reported Thursday.

The gasfield, known as Dabei III, boasts an estimated reserve of up to 130 billion cubic metres (4.3 trillion cubic feet), the China Daily newspaper reported, citing an unnamed source with the company.

It "will serve as an important back up supply source for the west-east gas pipelines", the source said, adding that the company will drill more appraisal wells to determine the final reserve.

The announcement of the discovery comes after PetroChina, already listed in Hong Kong and New York, won approval last month for a domestic listing expected this year which could raise up to 40 billion yuan (5.3 billion dollars).

PetroChina's parent said in August it will start building its second West-East natural gas pipeline in 2008, with gas transmission to come on stream in 2010.

The new pipeline will annually transport 30 billion cubic metres of natural gas imported from central Asian countries such as Turkmenistan and Kazakhstan, as well as gas produced in the Xinjiang region, the company said.

The newly discovered gasfield is potentially the third largest one in Xinjiang, after the Kela II and Dina II gasfields, Dai Jinxin, a researcher with a research institute affiliated with PetroChina told the newspaper.

Kela II and Dina II have proven reserves of 250 billion and 170 billion cubic metres respectively, the report said.