The US has approved the sale of Canadian oil firm Nexen to China's state-owned CNOOC, clearing the way for the deal to be completed.
The deal had been backed by Canadian authorities but needed US approval as Nexen has operations in the country.
There have been concerns over China's access to key US assets and regulators had previously blocked an attempt by CNOOC to buy a US-based firm.
The $15.1bn (£9.4bn) deal is China's largest foreign takeover.
Joshua Zive of Bracewell & Guiliani, a Washington-based lobbying firm said the approval for CNOOC's latest deal "is likely to be viewed as a positive development".
"That, in the current climate, is a moment of significance," he added.
However, a senior US lawmaker said that the government should block future deals if they did not benefit US taxpayers.
"Chinese government-owned oil corporations should not be allowed to drill for American oil in the Gulf of Mexico without paying a dime in royalties to US taxpayers," said Edward Markey of the House Natural Resources Committee.
Nexen's shares rose 2% after it announced the approval by the US regulators.
The firm said it now expects to complete the deal in the week beginning 25 February.