A quarter of Ireland's richest taxpayers - defined by the Revenue as having net assets worth more than €50 million - have a reportable income below the average industrial wage.
90 of the 480 so called High Worth Individuals managed by the Revenue in its Large Cases Division have an effective income tax rate that is lower than average income tax payers in the State.
In a report on how the Revenue manages the wealthiest individual taxpayers, the Comptroller and Auditor General says that on average these HWIs pay a higher effective rate than the average taxpayer - 39.2% for HWIs compared with 16.3% for the average taxpayer.
However, the tax they paid is highly concentrated, with just ten very wealthy individuals paying 85% of the income tax from the HWI group.
The C&AG report says Ireland’s definition of a High Worth Individual - assets in excess of €50m - is high by international standards.
In the UK it is the equivalent of €23m, in Australia €20m, Canada €30m while in Spain it is €10m in assets.
The threshold was examined in 2007 and 2011 and left unchanged, but the C&AG wants it reviewed again to see if this level is appropriate.
As well as 480 individuals, there are 140 trusts, partnerships and "certain companies and legal entities" which the revenue links to the wealthiest taxpayers in the Large Cases Unit.
One third of the HWIs earn their money in the real estate sector. 9% are active in agriculture, forestry and fishing. 5% are in the construction sector. Financial and insurance activities account for just 4%, the same as the arts, entertainment and recreation sector.
A study of the 2015 tax year found that €473m in income tax was paid by 334 High Worth Individuals - an average of €1.4m each.
However, when the nine highest taxpayers - described as "outliers" in the report - are removed - the average income tax paid amounts to €230,750.
The average income tax bill paid by all taxpayers in the State is €5,985.
HWIs also pay significant amounts of Capital Gains Tax, Capital Acquisition Tax and Stamp Duty.
These three headings made up some 39% of tax paid following Revenue interventions or audits of High Worth Individuals: Income tax accounted for 50% of the payments in these interventions.
As well as €475m in income tax, these same taxpayers paid €129.8m in USC, and €23.9m in PRSI.
A total of €93m in tax reliefs and credits was claimed by this group, mostly in the form of capital allowances and loss relief carried forward.
Ten individuals were able to claim tax relief in respect of maintenance, significant buildings and gardens relief, venture capital relief and trans-border relief. These tax breaks resulted in benefits to the ten taxpayers averaging €167,000 each.
140 HWIs - 42% of the total - had a taxable income of less than €125,000. This was below the level at which the Higher Income Earner Restriction (HIER) mechanism cuts in.
This restricts the amount of tax breaks an individual can claim.
Between 2012 and 2015 the amount of tax collected through this mechanism has increased, but the number of taxpayers it applies to has fallen.
The C&AG noted that during the period under review, a Qualifying Avoidance Disclosure programme (QAD) was in place, in which taxpayers who told the Revenue of tax avoidance schemes they were using could avoid penalty charges that would normally apply for using such schemes.
In one case a HWI had paid all the tax and interest due in his case before the QAD was introduced - which meant he was liable for penalties.
The report says "Revenue invited the taxpayer to make a QAD...which resulted in a refund of 20% of the interest which had already been paid, and the avoidance of penalties and publication" (of the taxpayer on the revenue defaulters list).
In another case Revenue allowed a HWI to claim tax relief on professional fees, which reduced his tax bill by €270,000 - even though Revenue was "without sight of the invoice and without proof of payment".
The C&AG also notes that Revenue "was unable to confirm that the professional fees had not been paid for tax avoidance advice".