It cost more than €786,000 to send the Taoiseach and other ministers around the world in private aircraft last year.
There were a total of 49 trips in 2019 – at average cost of €14,400 per journey.
While the government normally uses commercial flights for air travel, the Air Corps’ Casa and Learjet aircraft are used when necessary.
There were 46 missions on the Learjet last year, costing about €731,000.
The most frequent flier was the Tánaiste Simon Coveney, who made 17 journeys on the plane.
Meanwhile the Taoiseach Leo Varadkar made 15 trips.
The most expensive flights were for Mr Varadkar’s two-day trip to Egypt last February for the EU-Arab summit – which cost the taxpayer roughly €52,200 in air travel.
The next costliest use of the government jet was the Tánaiste's trip to Tel Aviv last month – which cost €48,800.
The Taoiseach took a further three trips on the lighter Casa aircraft, which set the taxpayer back more than €55,000.
Jack O'Sullivan is an environmental scientist in Co Westmeath.
“For many of these capitals it should be possible to use commercial flights,” he said.
“Commercial flights have a much higher number of passengers – if there is a good load factor as we call it – and have a much lower amount of carbon emissions per passenger kilometre.
“That should be availed of wherever possible.”
The total of just over €786,000 spent on the private flights is down 25% on last year.
A Government spokesperson said representing Ireland abroad is a “vital part of the work of any government.”