InterOil (IOC) on Sunday named Exxon Mobil(XOM) - Get Report as the previously unidentified, rival suitor for the Papua New Guinea-focused gas explorer and declared its offer to be superior to that of agreed bidder Oil Search.

Exxon Mobil offered $45 per InterOil share, paid in ExxonMobil shares. InterOil shareholders are also in line to receive so-called contingent resource payments of an additional $7.07 per share for each extra trillion cubic feet of gas equivalent discovered at InterOil's Elk-Antelope field above 6.7 trillion cubic feet up to 10 trillion cubic feet, the target said.

InterOil's board "in consultation with its legal and financial advisers, has determined that the ExxonMobil offer constitutes a "Superior Proposal," as defined in InterOil's arrangement agreement," with Oil Search. "InterOil has provided notice of such determination to Oil Search," it added.

The Irving, Texas  interloper is competing against a May agreement for Oil Search to buy InterOil, its partner in the Elk-Antelope project in Papua New Guinea, for $2.2 billion, a roughly 27% premium to the New York-listed target's undisturbed share price.

Oil Search owns both an interest in Elk-Antelope and in the nearby PNG liquefied natural gas project. It responded to its target's announcement on Monday by saying it is considering its position. Under the May 20 deal it has until July 21 to match Exxon Mobil's offer and stands to receive a $60 million breakup fee if InterOil goes with the U.S. bidder. Oil Search's bid partner, Total, of France, would receive 20% of that fee, said Oil Search, which noted that it would more than cover its costs.

"Total SA, with which Oil Search has a memorandum of understanding regarding the InterOil assets, is aware of these developments and Oil Search's right to submit a revised offer. The parties are in active dialogue and have the flexibility to submit a revised offer either during the three day notice period or after InterOil enters into an arrangement agreement with ExxonMobil," it said.

"Oil Search's board and management are committed to acting in the best interests of shareholders at all times and are presently considering their position. The proposal from ExxonMobil endorses Oil Search's view on the quality of the Elk-Antelope gas fields and the value of the Papua LNG Project. Given its existing material interests in both the PNG LNG Project and in the Papua LNG Project, Oil Search is well placed to participate in the potentially very significant benefits that are expected to arise from cooperation between, and/or integration of, the projects," it said, promising an update in "due course."

It also said it would delay a second-quarter update scheduled for Thursday in light of the development.

Total is effectively financing Oil Search's bid with $1.67 billion of secondary agreements to buy most of InterOil's assets,

TheStreet previously reported that Exxon Mobil's proposal was superior for a variety of reasons beyond its higher valuation, including InterOil's listing, like Exxon Mobil's, on the New York Stock Exchange, and additional potential cost synergies.

"People were very suspicious that Exxon would bid given the fact of how conservative Exxon is, cause this is anything but a conservative buy," Jim Cramer, TheStreet's founder, said Monday. "Now all in not that much money for them, but it's in New Guinea it's not in Texas."

Exxon Mobil operates the PNG liquefied natural gas field located close to Elk-Antelope and could derive efficiencies from owning stakes in both.

InterOil shares closed in New York on Friday up 19 cents at $47.61.

The Oil Search offer was based on 8.05 of its own shares per InterOil share, or A$58.36 ($44.29 ) per share based on Monday's close.

Oil Search closed up 3.9% at A$7.25 in Sydney on Monday.

Exxon Mobil closed up 17 cents at $95.12 in New York on Friday.