The cost of operating and maintaining 700 national monuments under the control of the OPW eexceeded €13m in 2019 but income was less than €6.3 million.
Kilmainham Goal operated at a profit of nearly €800,000, with more than €2 million taken in in admissions last year.
The Rock of Cashel made a profit of nearly half a million euro, with over €1.5 million income.
But several other sites operated at significant losses.
Less than 50 sites operate with a guide service, some are closed or are free.
The OPW says it charges admissions to certain heritage visitor sites in its care but doesn't have a very commercial pricing strategy.
It says these sites are mainly a public cultural asset.