The Health Service Executive has spent over €114m this year on agency staff up to September, according to figures released to Sinn Féin’s health spokesperson Louise O'Reilly.
Agency staff are hired to plug staffing gaps, but can be significantly more expensive than direct employees.
However, they do not enjoy job security, nor do they receive pension contributions.
The hospitals with the highest agency spend so far this year were: the Midland Regional Hospital Portlaoise (€8.143m), University Hospital Limerick (€7.851m), Cavan Monaghan General Hospital (€6.970m), the Midland Regional Hospital Mullingar (€6.918m), Naas General Hospital (€6.007m) and University Hospital Kerry (€5.836m).
Up to September of this year, the HSE agency spend for medical and dental staff came to over €49m, with the highest individual spender being the Midland Regional Hospital Portlaoise at almost €5.5m.
For agency nursing staff the HSE has spent just short of €22m. The highest outlay was at Cork University Hospital (€2.069m).
Agency staff delivering support services cost the HSE almost €32.7m, with the highest spend at Our Lady of Lourdes Hospital in Drogheda (€2.469m).
Paramedics recruited from agencies cost €6.547m across the health service - with the biggest bill at Our Lady of Lourdes Hospital (€684,000).
Agency management and administrative staff were also recruited at a total cost of €3.712m - with the highest cost at University Hospital Limerick (€603,000).
In total, from 1 January 2010 to September of this year, the HSE figures reveal a total agency spend across all grades of €1.174bn.
In responding to Ms O'Reilly's Parliamentary Question, the HSE said that the agency pay cost is under constant review.
It said this expenditure should be considered in the overall context which includes increasing demand for services, and the impact of earlier constraints on recruitment in the public service.
It also cited ongoing challenges in relation to the recruitment and retention of clinical staff, and the actions necessary to ensure compliance with statutory limitations on working time.
It notes that agency personnel are only used where there is a difficulty in recruiting and employing hospital staff, and where there is a short-term critical need, or to permit flexibility to allow for variations in activity, or to meet patient demand needs.
In 2010 the cost of agency personnel was around €82.5m, but in 2011, that rose to €95.5m.
The following year, the figures fell slightly to €95.8m, but increased significantly in 2013 to €125m during the moratorium on recruitment.
There was another huge leap in 2014, when the spend on agency staff rose to €187m.
By 2015, it had fallen to €159m, with a further slight fall in 2016 to €157.7m.
The agency spend was almost static in 2017 at €157.5m - with the 2018 tally reaching €114m by the end of September.
Deputy O'Reilly has criticised the amount spent on agency staff, describing it as "colossal".
In a statement, she said: "The over-reliance on the use of costly and more expensive agency staff has escalated under this Government. The colossal amount of money spent on agency and locum staff constitutes a financial waste by the State because they are much more expensive than directly employed staff".
"The reason hospitals are forced to rely on this staffing mechanism to fill vacant posts is because the Government has failed to address the recruitment and retention crisis."
"Health service staff and their unions have consistently reported working conditions, facilities, supports, training opportunities and pay as the cause of the recruitment and retention crisis, and until these issues are addressed the crisis will continue and these staggering sums of money will be wasted on agency spending."