The Treasury has released the briefing it gave to incoming Finance Minister Bill English after the election, featuring a comparison between the effective tax rates on various asset classes.

It shows that despite recent changes to the tax system, housing is still a much more attractive option tax-wise than shares or bonds.

At a 33% marginal tax rate Treasury calculated that debt instruments (mainly bonds) have a real effective tax rate of almost 50%, with domestic shares at just over 45% and foreign shares slightly lower at about 42%.

Meanwhile, rental property has an effective tax rate of only 25% and owner-occupied housing isn't taxed at all.

"The Treasury is continuing to examine a range of options for taxing capital more evenly, and at lower rates," the report said.

"Key questions that will need to be addressed before making decisions on tax reforms of this magnitude include the size of the economic benefits and fiscal costs, administrative feasibility, and implications for distributional equity."

PWC tax partner and Tax Working Group member Geof Nightingale said the report was "advocating quite strongly for a capital gains tax" even though it never used the exact words.

"The theme through the document is we are still not doing enough to address the savings imbalance."

He said the chart used by Treasury wasn't unfamiliar; the Tax Working Group came up with something similar, although changes to rules on building depreciation have changed the figures slightly.

Nightingale said the exact numbers were "sensitive to the assumptions used" and, to complicate the picture even more, the same investment by the same investor can be taxed in different ways depending on what investment vehicle is used.

"For an investor the same debt instrument can be taxed at different rates depending on who holds it," he said.