Some push-button coffee machines are turning over a staggering €1m-a-year each for busy service stations.
Vast profits are being made by selling the commodity coffee and charging €2.70 for it.
And campaigning broadcaster Philip Boucher-Hayes revealed: "Petrol stations are not just making a killing, it's a massacre."
The latest episode of his RTE series What Are You Eating? lifts the lid on Ireland's snacking obsession.
A huge 42pc of us have a drink with every snack we eat - with coffee being one of the most popular. Three-quarters of the population drink coffee, with one in every 10 people drinking five or more cups a day.
Gourmet coffees are now incredibly popular but Mr Boucher-Hayes discovered they do not make a fraction of the profits of a cup of joe from a filter machine in a service station.
Coffee expert Colin Harmon estimates a €1m a year push-button machine would make €900,000 profit before staff costs were taken into account. "It's insane - that's just a push-button espresso machine. It's commodity-grade coffee.
Mr Harmon, owner of the 3FE speciality cafe in Dublin, said: "A bog-standard cup of coffee out of a petrol station will cost you about €2.75. We source some of the best coffees in the world so our base price is about €3.50 and we still make a profit."