However it will only join, and free carry the junior Melbana (20%) if it can find a third party to farm-in.
Should this happen, Melbana will not be required to fund the first exploration well on the permit, Beehive-1.
Initially Total and Santos each had an option to take 40% and last month Santos exercised its option and Total did not, despite jointly funding a 3D seismic survey over the area.
Santos will need to find a farminee by March and if it can't full interest will revert back to Melbana. The deal is also conditional on the junior pushing back the date of the well, required by the end of next year under the terms of its work program.
If Santos finds another partner for the project, it has agreed to complete an application for an environmental permit to drill the proposed Beehive-1 well.
"We're pleased to continue to work cooperatively with Santos given the commitment they've shown to Beehive," Melbana chairman Andrew Purcell said.
"This variation to our agreement with Santos takes us a critical step closer to drilling the largest undrilled structure in Australia."
Despite Purcell's cheer Santos' investor briefing day on Tuesday contained no mention of the prospect, despite the company's focus on the offshore north of Australia after its Quadrant Energy and ConocoPhillips' Northern Australian assets acquisitions.
"There's a lot of interest, but we can't talk to anybody yet," Purcell told Energy News of other possible farminees in October after Total pulled out.
"We've been approached by many credible parties. Obviously it would have been better if Total came in but having Santos there … they're very interested in the property."
Beehive has been one of Melbana's flagship prospects beyond its work in Cuba or its now spun off onshore New Zealand Pukatea project, but development has always been contingent on two much larger, busier partners farming in.
Beehive has a best estimate prospective resource of 388 million barrels of oil equivalent and a high estimate of 1.6 billion barrel oil equivalent prospective resource, as assessed by independent exports McDaniel and Associates.
Separately today Melbana yet again extended the deadline of its takeover of Metgasco.
In September Melbana launched a hostile, all-scrip takeover for Metgasco, which has interests in Byron Energy's South Marsh 74 project in the Gulf of Mexico, and more recently has entered the Cooper-Eromanga and Perth basins.
Metgasco's board urged shareholders not to approve any offer by Melbana due to "significant risks associated with the Beehive prospect."
"The significant risks associated with the Beehive prospect, as outlined in Metgasco's target statement, remain and are arguably highlighted by a global E&P major such as Total electing to withdraw from the project despite having funded seismic acquisition and interpretation," it said in October.
The company noted that even if Santos took its 80% interest, the permit would expire in December 2020 without a well, and rig availability could be an issue.