Prime Minister Malcolm Turnbull will reportedly announce an 80-cent GST floor for Western Australia, but the premier says he will believe it when he sees it.
Mr Turnbull will take his solution to the GST revenue distribution formula to cabinet shortly, and is expected to announce it at the Liberal state conference in Perth on August 11, The Sunday Times reports.
The top-up, which would provide WA with an additional $5 billion over three years, would come from consolidated revenue in a bid to appease Tasmania, South Australia and Queensland.
"Show us the money. No more promises, no more talk, actually do it and provide it immediately ... we'll believe it when we see it," Mr McGowan told reporters in Perth on Sunday.
The federal government is currently considering the Productivity Commission's review of the GST formula.