The source told PNGIndustryNews.net that Exxon failed to close a deal and questioned why a press release was not made.
"It's dead," the source said, before indicating that other pre-selected bidders have the opportunity to approach InterOil.
"They [InterOil] have opened it up again to others this morning."
ExxonMobil has not commented on the matter.
"It is not our practice to comment on commercial discussions," a spokesperson said.
Yet an InterOil spokesperson said negotiations between Exxon and InterOil were ongoing, although he needed to make enquiries to see if they were still on an exclusive basis.
The exclusive talks were first announced in late May with PNG Prime Minister Peter O'Neill telling Parliament they would last for up to 60 days.
While PNGIndustryNews.net understands there was a time extension, the source indicated it too had expired.
Exxon was aiming to acquire at least 4.6 trillion cubic feet of gas from the Elk-Antelope field to fuel a third train expansion of the PNG LNG project it operates.
However, Petroleum Minister William Duma along with Gulf Province parliamentarians had since campaigned against piping the Elk-Antelope gas outside of the province, providing an obstacle to Exxon's plans.
At least two other supermajors previously made bids over the Elk-Antelope asset.