Australia touted itself as a "global energy superpower" after shrugging off diplomatic tensions with China to sign a record $41.3 billion resources deal.
In Australia's biggest ever trade agreement, PetroChina ordered 2.25 million tonnes of liquefied natural gas (LNG) a year over two decades from ExxonMobil's share of the still-undeveloped Gorgon plant off the country's west.
The huge contract comes despite weeks of deteriorating ties over China's detention of a Rio Tinto mining executive and Australia's decision to allow a visit by leading dissident Rebiya Kadeer.
The signing ceremony was held behind closed doors in Beijing and announced by Australia's Resources and Energy Minister Martin Ferguson late on Tuesday.
"The ExxonMobil 50 billion (Australian) dollars LNG export contract to China represents the biggest export contract in the history of Australia," he said, according to public broadcaster ABC.
"It also potentially underpins the biggest single construction project in the history of Australia, which could see 6,000 workers on the job at the peak construction period."
Ferguson said the deal, which follows ExxonMobil's 21 billion US dollar sale of Gorgon LNG to India's Petronet last week, showed Australia had a future as a "global energy superpower".