Nexen (TSX:NXY) announced Sunday the two companies agreed to extend the deadline as they were still awaiting U.S. regulatory approval.
However, it stressed that the closing can only be extended a maximum of 75 business days beyond the original deadline of Jan. 31.
The federal government approved the takeover in December. China, Britain and the European Union have also given their go ahead for the agreement.
But U.S. approval is needed to complete the deal because Nexen has operations in the Gulf of Mexico.
Nexen, meantime, says it will postpone the release of its fourth-quarter and annual results because of the delay.