Former NSW Labor heavyweight Eddie Obeid, his son Moses and former Minister Ian Macdonald deliberately engaged in a mine licence conspiracy for significant financial gain, a court has heard.

Key points: The trial is expected to last for six months and hear from more than 50 witnesses

The trial is expected to last for six months and hear from more than 50 witnesses Among them will be a former Premier, and several journalists

Among them will be a former Premier, and several journalists The court heard Mr Macdonald wanted to repay Eddie Obeid for past favours

Eddie Obeid, 76, Moses Obeid, 50, and Mr Macdonald, 70, are on trial accused of conspiring over a coal exploration licence issued over the Obeid family farm "Cherrydale Park" at Mount Penny in the NSW Bylong Valley.

At the time Mr Macdonald was the NSW resources minister.

Sitting side-by-side in the dock of the Supreme Court, the former ministers stood separately to formally plead "not guilty" when their conspiracy to engage in misconduct charge was read out by a court official.

Prosecutor Sophie Callan said the three men entered into a conspiracy knowing Mr Macdonald would breach his confidentiality and impartiality obligations to benefit Obeid family interests.

She said at the time "coal prices were escalating around the world" and the NSW Government was "otherwise under significant budgetary strain".

The prosecutor said the crown case was circumstantial and would involve more than 50 witnesses including members of the NSW Labor Party and staff from the Department of Primary Industries.

The six-month trial will also hear evidence from Federal Opposition Leader Anthony Albanese, former Premier Morris Iemma, journalists, forensic accountants and handwriting experts.

Ms Callan said the crown would provide evidence of a strong personal and working relationship between Mr Macdonald and Eddie Obeid.

"You will see diary entries of meetings," she told the court.

Ms Callan said at the time the mine licence was issued Mr Macdonald was in his final term in office and motivated to repay Eddie Obeid for "past political favours" and "to secure future favourable treatment".

She said there would be evidence of a 2006 meeting of Labor Party officials at the Noble House Chinese restaurant in Sydney's CBD just before a state election to decide Mr Macdonald's future.

The court heard at that meeting it was discussed that Mr Macdonald would resign after spending a decade in Parliament.