BEIJING, July 15 -- China's biggest oil firm PetroChina will invite major foreign oil companies to help the State-owned company explore for oil and gas in as many as nine blocks in Northwest China's Xinjiang Uygur Autonomous Region.

    The new blocks are mainly distributed throughout the southwestern, central and eastern parts of the Tarim Basin, which has proven reserves of 6 billion tons of oil and 8 trillion cubic metres of natural gas, the Beijing-based company said in a statement on its website.

    The move marks the most significant co-operation with foreign giants in oil and gas exploration in the past 12 years, analysts said.

    More gas discoveries in the northwestern region will increase source supplies to the 3,800-kilometre-long natural gas pipeline, which extends from Xinjiang in the west to coastal cities in the east, PetroChina said.

    PetroChina will partner with foreign firms through product-sharing contracts and "several major international oil companies" have expressed interest, the statement said, without elaborating on which firms.

    The overseas-listed company said it would enlist state-of-the-art technology worldwide to tap the huge energy potential in the northwestern region.

    Yuan Xinxiang, a PetroChina spokesman, told China Daily on Friday that the listed firm, instead of the parent company China National Petroleum Corp (CNPC), would handle the nine new blocks in Xinjiang. But he declined to further disclose exactly when the company would start the tendering, although the company statement said "in the short term."

    Foreign oil companies including Exxon Mobil, Total SA, Chevron and Royal Dutch Shell Plc were not available for comments on Friday.

    "I am not aware of the new information and I could not comment," said a Shell official.

    Over the past 20 years, PetroChina and its parent firm CNPC have teamed up with as many as 46 overseas oil companies such as Total, ConocoPhillips and Shell to work on 16 oil and gas projects in China. These joint efforts have produced 22 million tons of oil and 2.5 billion cubic metres of natural gas so far, the Chinese oil firm said.

    Covering an area of 560,000 square kilometres, the Tarim Basin represents one of the country's three big basins with oil and gas resources exceeding 10 billion tons. With 16 years of exploration and development, annual production in the northwestern basin reaches more than 10 million tons of oil equivalents, PetroChina said.

    China has vowed to step up exploration efforts across the country to secure sufficient energy supplies to fuel its fast-growing economy.

    PetroChina's domestic rivals Sinopec and China National Offshore Oil Corp both announced big gas discoveries in China recently.

    Sinopec, also Asia's biggest oil refiner, last week said they aim to secure up to three medium- or large-sized natural gas finds with reserves of 60 billion cubic metres in Northeast China by 2008, after it made a major gas discovery in the region.

    The Ministry of Land and Resources said on its website on Thursday that a gas discovery in the northern part of the South China Sea might hold more than 100 billion cubic metres of natural gas.

    Xiao Zongwei, a China National Offshore Oil spokesman said on Friday it was the same well sunk by Canada's Husky Energy Inc and its reserve figures have yet to be verified.

    Husky, which is participating in China's oil and gas exploration under a product-sharing contract with China National Offshore Oil, announced a major gas discovery in June in the Liwan 3-1-1 field in the Zhujiangkou basin, 250 kilometres (155 miles) south of Hong Kong.

    A Dow Jones report last week said Shell had submitted a development plan to PetroChina to help secure production in the largest gas field in Southwest China's Sichuan Province with 58 billion cubic meters of proven reserves.

    Lim Haw Kuang, chairman of Shell China, declined to comment on Tuesday.