A new report on the activity of NAMA says the agency could have raised an extra €18bn euro for the tax payer.
It's claimed the agency failed to realise a better return because it sold off their assets too quickly.
The research has found that 11 major sales to investment funds were then 'flipped' by the buyers with an average profit of 47%.
It says the taxpayer lost more than €300m on those transactions alone.
The study was conducted by Economist Jim Power and Lisney Estate Agency and commissioned by the Property Developer David Daly.
Speaking about the research, Jim Power said "In the context of the recovery of both Irish and global property markets NAMA’s stated return of a maximum €2.3bn on an investment of €31.8bn seems significantly lighter than would be expected.
"It would appear that NAMA has been aiming to recover its initial investment of €31.8bn and not the €74.2bn of debt owed to the 5 main banks, as was its original remit.
"As such, in excess of €40bn has been left behind by NAMA at the expense of the taxpayer."
David Daly, who commissioned the research said "It’s clear that NAMA’s fire-sale of the nation’s property assets has allowed vulture funds to make a killing at the taxpayer’s expense.
"The agency would have fared better had it opted for a medium to long-term, commercially savvy approach over its knee-jerk, panicked and inexperienced reaction."
