More than 43,500 public patients missed out on treatment to private patients between 2015 and 2016.
The majority of consultants should only be undertaking 20% private work but RTÉ Investigates found that consultants in 14 public hospitals are exceeding this limit.
This means that public patients are having to wait longer for procedures.
Consultants are permitted to do extra paid private work within public hospitals and some are also entitled to work in other private hospitals and clinics.
UCC Health Economist Brian Turner told RTÉ that the lack of co-location of public and private hospitals together is a big problem.
He said: "It clearly reduces the availability of these consultants for public patients, because if they are offsite it will obviously take time for them to get back onsite.
"Whereas if they were onsite, even if they were dealing with private patients, at least they would be available at notice to treat public patients, if required."
The Irish Hospital Consultans Association said that it can confidently state that the overwhelming majority of consultants are "working well beyond their contracted hours in an effort to provide care for patients in an under resourced health care system".
The IHCA President, Dr Thomas Ryan, said that each year hospital consultants throughout the country treat a quarter of a million more patients compared with a decade ago, despite the fact hospitals now have 12% fewer in-patient beds.
The Association said that while it cannot comment on the individual cases referred to in the reports on the programme, there is a mechanism in the Consultant Contract which is available to hospital management to address such matters.
Dr Ryan said that the vast majority of patients are admitted to public hospitals through emergency departments and, as a consequence, consultants cannot control the mix of patients in terms of their public or private status.
In addition, Dr Ryan said that it is widely acknowledged that the methods used in hospitals to measure public patient to private patient ratios are "both inaccurate and unreliable".
He said: "This was identified as a problem in an independent management report commissioned by the HSE in 2007 during the Consultant Contract negotiations.
"In 2011 the IHCA and the then HSE CEO agreed that those serious flaws needed to be rectified, but that has not yet happened."