The latest figures in the Mid-Year Economic and Fiscal Outlook (MYEFO) show that the "estimated aggregate value of tax in dispute as at October 31 2014, for which a provision has not been made, is $5.1 billion".

This figure is up from $4.6 billion in disputes reported in the May budget, but down from $7 billion reported in the MYEFO papers from a year ago.

The ATO has mounted some big cases against multinationals including Chevron, which are still pending.

Tax Commissioner Chris Jordan has repeatedly vowed to only take cases the ATO thinks it can win to court, rather than waste time on lengthy legal disputes. This explains the dramatic fall in disputes over the past year.

The 2014-15 MYEFO papers said that the $5.1 billion figure could not be taken as an indication as a loss to government revenue, as disputes were ongoing.

"At any point in time the Australian Taxation Office is involved in a range of dispute resolution processes, including litigation, relating to tax disputes," the papers said.

"Details of the outcome of dispute resolution processes are uncertain until a court ruling is made and/or an agreement is reached with the taxpayer. As a result, in most cases it is not possible to estimate with any reliability the likely financial impact of current disputes."

According to the ATO's latest annual report, over the past 12 months, the tax office has settled 393 cases for a combined total of $2.6 billion.

"This is the highest number of settlements reached in any year for the ATO," said PWC tax controversy partner Ashley King.

"It is also the highest amount the ATO has collected from settlements of tax disputes in any year, evidence that it has not necessarily been an easy resolution path for taxpayers."

Mr King said it was all evidence of Mr Jordan's new approach to dispute resolution, which included cleaning up old disputes, but where there is conflict, taking companies to court faster.

Clayton Utz tax partner Niv Tadmore said the Tax Office and companies were now having more "efficient and constructive" engagement than was the case in previous years.

"On the one hand, the ATO audits go deeper and are more forensic and focused, and on the other hand, the ATO encourages the resolution of these disputes out of court in a more efficient and constructive way," Mr Tadmore said. "The new independent review function introduced by the Commissioner is an example on point."