As of February 2023, the average cost of gas in Ireland is €1.67 per liter. Note, 1 gallon = 3.78 liters. This means that gas costs approximately $6.71 per gallon. It's also called petrol in Ireland, not gas. Opting for a diesel car rental in Ireland over petrol might help you save money too. Applegreen gas stations have a good reputation for providing the cheapest gas. But when you're in the countryside, you might not have a choice of gas stations as they can be sparse.