The main who has led Bougainville for the past five years is on course to continue in the role as his lead grows with the vote count well underway in Buka.
John Momis, who has been involved in Bougainvillean politics since before it was established as a Papua New Guinea province more than 40 years ago, has taken an approximately 17,000 vote lead over Ishmael Toroama in second place.
Mr Toroama is the former commander in the Bougainville Revolutionary Army which fought for the region's independence in a bitter and violent civil war.
On Monday evening Mr Momis had more than 22,000 votes with Mr Toroama on just over 5,000.
In third place is former national government cabinet minister, Sam Akoitai.
Nine men ran for president.
Meanwhile 12 of the 39 seats in the new parliament have now been declared.