Pump prices have now fallen by 25c since June last year.
A petrol price war has broken out after one of the largest fuel retailers in the State cut its prices by 3c a litre.
The move means that the cost of motor fuel is now on a par with the cost of a litre of bottled water.
Applegreen is to reduce its prices back to what it said were 2009 levels at its 133 forecourts.
The group said the lowest price for a litre of petrol would now be as €1.16 at its forecourts, with diesel as low as €1.01.
Price cuts by Applegreen are expected to prompt a response from other big petrol retailers such as Topaz, Esso, Texaco and Maxol, along with independents.
A spokesman for Topaz said the company was passing on the fall in oil prices to consumers as they happened.
Chief executive of Applegreen Bob Etchingham said pump prices have now fallen by 25c since June last year.
"Falling crude oil prices has seen petrol and diesel pump prices drop significantly over the past number of months. This is really positive news for the driving public in Ireland," he said.
The moves comes as crude oil prices continued to fall below $30 a barrel on world markets yesterday, with predictions that oil will drop to $20, with some investors suggesting a $10 price.
Dublin garage Emo in Mount Brown in Kilmainham became one of the first in the capital to sell diesel below €1. Earlier in the week, service stations in Mayo dropped their prices to this level.
The Irish Petrol Retailers' Association (IPRA), which represents 550 independent fuel retailers, said its members would respond to the price cuts by larger petrol retail groups.
David Blevings of the IPRA said: "At the end of the day they all set their own price, but independent petrol retailers will respond. They have to move down to compete."
He said drivers would benefit from more price cuts, especially if predictions by international investment bank Goldman Sachs that a barrel of crude would fall to $20 were correct.
Asked how low prices at the pumps would go, Mr Blevings said: "Who knows? We are in uncharted waters. How long it goes on we don't know, but prices do have further to fall."
AA Ireland director Conor Faughnan said pump prices would be even lower if taxes had not been increased five times in the emergency Budgets by a succession of governments since 2008. He said this had added 20c to the prices of both fuels for drivers.
This time last year motorists were paying as little as 122.8c per litre of petrol and 117.8c for diesel.
The average price of a litre of petrol is now 125.9c, with diesel at 109.9c across the country, according to comparison site Pumps.ie.
Via Independent.ie