Two key witnesses are today expected to give evidence at a New South Wales corruption inquiry into rigged mining tenders.

The Independent Commission Against Corruption (ICAC) inquiry into allegations former Labor Minister Eddie Obeid stood to make millions from inside knowledge from former mining minister Ian Macdonald, is sitting for another three days to hear from witnesses that were previously unavailable.

One of them is Ian Macdonald's business partner John Gerathy who last month told investigators he was in hospital.

The inquiry has heard that documents in his handwriting suggest Ian Macdonald stood to receive up to $4 million as a kick back from a coal deal.

Another witness - the Obeid family accountant Sid Sassine has been overseas.

The ICAC has heard allegations he helped channel millions from coal deals through complex family trusts.