Treasurer Wayne Swan took responsibility for his department's miscalculation of commodity prices when the RSPT was planned.

"It is true that the Treasury under-estimated where that was and I accept responsibility for that as the Treasurer," he said.

Mr Swan released updated budget estimates yesterday, taking in Treasury's new approximates for commodity prices that would boost the budget profits by $4.9bn over the next four years. The Treasurer confessed that had the higher prices been implemented to the RSPT, it could have earned up to $24bn.

Meanwhile, Coalition finance spokesman Andrew Robb called the new commodity forecasts "spurious" and said it was not convincing that they would more than double projected income from the resource tax but do nothing for the rest of the economy.

"To go to the people with what I think are the rosiest set of assumptions imaginable is to me to the point of being deceitful," Mr Robb said.

But according to Mr Swan, Treasury's new approximates for commodity prices considered information provided to the government during negotiations with mining giants BHP Billiton, Rio Tinto and Xstrata.

"We did have a much more productive, informed and detailed discussion between Treasury and major mining companies about not just current prices and volumes but current prices and their likely trends over time and their likely volumes over time," he said.

"That led Treasury to upgrade substantially its forecasts for commodity prices and that's what has occurred."

The Treasurer said it had never been the government's intention to collect so much money from the mining sector, and that the government's move to spend all the proceeds from the MRRT on other tax and infrastructure measures would be sustainable, even if commodity prices slumped in future.