A binding heads of agreement was struck in late April and a farm-in agreement has since been executed.
InterOil said the terms were "materially the same" as those it previously announced.
It means the deal may be worth up $345 million even if PRE carries 25% of InterOil's upstream expenditure at the Triceratops-2 well plus funding for "six additional wells in the Triceratops structure".
But InterOil stressed that the full farm-in transaction was dependent on various conditions within 18 months, including PNG government approval.
"Additionally, PRE has the option to terminate the farm-in agreement at various stages of the work program and to be reimbursed up to $US96 million of the $116 million initial cash payment, which does not include carried costs, out of future upstream production proceeds," InterOil said this week.
"We look forward to completing the Pacific Rubiales farm-in and to accelerating appraisal and development of the Triceratops gas and condensate field in Papua New Guinea," InterOil chief executive officer Phil Mulacek said.
"We are very pleased to be partnered with InterOil and its management on what we believe to be a world-class gas and condensate trend and which provides us with the strategic opportunity for early-stage large resource capture on the doorstep of the world's fastest growing primary energy markets," PRE CEO Ronald Pantin said.
Pacific LNG Operations, one of InterOil's existing JV partners, will earn 25% of PRE's payments relating to the Triceratops structure under the deal, along with a commission fee of 2.5% for cash payments made by PRE which are not part of its agreed carrying commitments.