US energy giant ExxonMobil has placed an offer to acquire Papua New Guinea-focused energy company InterOil for $2.5bn including debt, rivaling a takeover bid made by oil and gas firm Oil Search.

The bid by ExxonMobil comes against an offer made earlier by Oil Search, with which French oil major Total signed a memorandum of understanding (MOU) regarding the InterOil assets.

As per the MoU, Oil Search will divest 60% stake acquired from InterOil in PRL 15 and 62% of InterOil's exploration assets to Total.

Oil Search said in a statement: "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."

ExxonMobil will offer $45 worth of its own shares for each InterOil share as well as a payment of $0.90 per million cubic feet equivalent (mcfe) for resources of more than 6.2 trillion cubic feet at the Elk-Antelope gas field, which is claimed to be one of Asia's largest undeveloped gas fields.

Oil Search, however, earlier offered $40.25 for each InterOil share.

Oil Search said that the proposal endorses its view on the quality of the Elk-Antelope gas fields and the value of the Papua LNG Project, which is operated by ExxonMobil with co-venturer Oil Search.

The integrated project comprises gas production, processing and liquefaction facilities, as well as offshore and onshore pipelines.

InterOil has assets including Elk-Antelope gas field in the Gulf Provinceand exploration licenses, which  cover an area of about 16,000km2.

Image: ExxonMobil intends to expand its operations in Papua New Guinea. Photo: courtesy of supakitmod/