The HSE spent €13.6 million euro on private ambulance services last year.
According to freedom of information figures, it's a 37% increase on the previous year.
The HSE's National Ambulance Service mainly deals with emergency calls.
Private ambulances are mainly used by hospital groups to transport patients who are less seriously ill.
In 2020, €9.9 million was spent on private ambulance services by HSE hospitals - rising to just under €13.6 million last year.
Lifeline Ambulance Service got €4.3 million in 2021 - the highest amount.
David Hall is its chief executive - he says private providers are needed.
"It's very easy and very politically expedient to be able to say we shouldn't be spending money on private ambulance services - that's fine.
"But then what happens patients in the meantime. Do we wait for a certain amount to die and then we change our policy?
"Maybe the Oireachtas Committee on Health may be the entity to look into this and find out, why is it a State body is gambling with lives, and not utilising ambulances the length and breath of the country that could be deployed to save lives."
The HSE says the big difference in expenditure between 2020 and 2021 was down to Covid-19.
It says private providers helped with testing and vaccination.