The federal government admits some states might not sign up to a national compensation scheme for victims of institutional sex abuse.
The states are concerned about what a royal commission estimates is $613m worth of funder-of-last-resort costs after institutions cease to exist.
"I'm fairly confident that it will be an overarching majority of states and territories, but we're still in ... a slightly grinding process of negotiating that outcome," Social Services Minister Christian Porter told ABC radio on Thursday.
He said it was the single, most complicated legal issue he'd ever dealt with, and a second draft of the proposed legislation would be distributed shortly.
"I'm very confident that we will have a lot of the states opting in," Mr Porter said.
The Commonwealth doesn't have the legal power to compel the states or affected institutions to take part in the scheme.
But it can compel the ACT and the Northern Territory.
NSW is refusing to commit to the scheme, opting to wait for details about costs and how the system will work. Queensland and Victoria want more information.
Mr Porter, who is meeting with institutions on Friday to discuss their concerns about compensation, said the scheme was being designed to benefit victims.
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