NSW taxpayers have missed out on "tens of millions of dollars" in revenues because of an allegedly corrupt scheme that was designed to net the Obeid family $100 million, an investigation has been told.

In his opening address, counsel assisting, Geoffrey Watson, SC, told the Independent Commission Against Corruption that the scheme could represent corruption "unexceeded since the days of the Rum Corps".

"The effects of the minister's [Ian Macdonald's] decision are that some of our coal assets - assets which could have created revenue of tens of millions of dollars - have passed to the ownership of third parties for a comparatively trivial return for the people of NSW," Mr Watson said.

These assets have been "given away to friends, political supporters and business associates of the minister".