China National Offshore Oil Corporation (CNOOC) has signed a multi-billion dollar deal with Australia's BG Group to buy millions of tonnes of gas.
Under the deal, which still need government approval, CNOOC will buy 3.6m tonnes of liquefied natural gas a year for the next 20 years.
Reports suggest the deal could be worth up to 80bn Australian dollars ($73bn; £49bn).
China's demand for gas is continuing to surge as its economy grows strongly.
"This deal is further evidence of Australia's vital role in global energy security in the 21st century," said the country's Resources and Energy Minister Martin Ferguson.
The 72m tonnes of gas are due to come from BG's gas plant on Curtis Island.
The two companies agreed a preliminary deal last year.
Earlier this month, CNOOC signed $3.1bn (£2.1bn) for a 50% stake in Argentine oil and gas group Bridas Corporation.
Keep making Australia a rich country china! While the poor in china keep getting poor hahaha