SHANGHAI, Sept. 6 -- PETROCHINA Co signed a deal worth up to US$37 billion with Woodside Petroleum Ltd today to buy liquefied natural gas from offshore Western Australia, in the company's second large LNG purchase this week.

Under the initial agreement, Woodside will sell two million to three million tons of LNG a year from the Browse project to PetroChina for a period of 15 to 20 years, the Perth-based company said.

``The full contract has the potential to bring in revenues in the order of A$35 billion to A$45 billion (US$29 billion to 37 billion) into Australia,'' Woodside Chief Financial Officer Mark Chatterji said in a statement, potentially making it the largest single export deal by an Australian firm.

The agreement is subject to conditions including a final investment decision on the Browse project and relevant government approvals.Supply of Browse LNG is set to start between 2013 and 2015.

The announcement came just days after PetroChina signed another LNG deal this week in Australia, where President Hu Jintao is paying a visit along with a delegation of Chinese investors.

On Tuesday, PetroChina signed a 20-year supply contract with Royal Dutch Shell Plc for LNG from the Gorgon project in Western Australia. The Shell deal is expected to give a confidence boost to the stalled Gorgon project, led by American oil giant Chevron Corp, on which a final investment decision hasn't been made.

PetroChina will ship the LNG back to China, where the super-cooled gas will be regasified at its LNG terminals. PetroChina has to secure supply for its planned three LNG terminals along China's coast.

China National Offshore Oil Corp started importing LNG to China's first such receiving terminal last year, under a 25-year contract secured in 2002 with North West Shelf project, also managed by Woodside.

CNOOC's contract price signed then was at near-record low levels. LNG term prices newly agreed by PetroChina are believed to rise sharply amid robust demand in a global seller's market. Pricing details of PetroChina's contracts were not disclosed.

China wants to use a larger portion of natural gas to produce energy consumption in order to reduce pollution.