One-in-six petrol pumps around the country is not giving motorists what they pay for.
Tests on petrol pumps in garage forecourts have found that 16pc are dispensing inaccurate levels of fuel, the Irish Independent has learned.
The unpublished report reveals that some motorists are being overcharged while others are getting more fuel than they paid for.
The disclosure comes as petrol prices continue to rise -- hitting €1.71 in many places around the country and adding considerably to the cost of running the family car.
The survey on petrol-pump accuracy was carried out by the AA on more than 170 pumps in Dublin, Wicklow, Cork, Kilkenny, Meath, Westmeath and Limerick.
In most cases the errors made were in favour of the customer. But there were also a substantial number of instances where the driver got less fuel than was paid for.
Legally, a petrol pump should start dispensing fuel when the meter is at zero, and should accurately dispense the amount displayed on the pump to within plus or minus 0.5pc.
However, the tests found that in 16pc of cases the pumps were out by at least 1pc.
And in 10 cases, the pumps were out by more than 2pc.
Of the petrol pumps tested, 10pc were giving out too much petrol, while 6pc were dispensing too little.
Even a mistake of 1pc in favour of a garage would cost a motorist almost €1 every time the tank is filled.
The average garage sells between 30,000 and 50,000 litres of fuel per week.
The AA stressed that the garages involved had all co-operated with the tests, and there was no suggestion of any deliberate overcharging.
It said the problem was with the pump meters going out of calibration over a period of time and not being properly reset.
After being shown the test results, many garage owners were "very shocked", the AA said.
All of the them committed to having the pumps recalibrated and properly re-set.
AA corporate affairs manager Conor Faughnan said yesterday: "We want to be sure that motorists are not losing out. With prices so high, the Irish motorist wants to be sure that a litre is a litre.
"Given that a driver doing any sort of higher mileage is likely to be using 3,000 litres of fuel a year, and paying over €5,000 for it, wants to be sure that they are getting a fair deal," he added.
The National Standards Authority of Ireland (NSAI), which polices petrol-pump equipment, has separately found cases of deliberate tampering with pumps.
The authority recently brought the first successful prosecution of a service station for using fuel pumps which "under-measure" the amount of petrol and diesel being sold to motorists has taken place.
Last November, the service station -- trading as One Oil on Usher's Quay in Dublin -- pleaded guilty to 12 charges of breaching the Metrology Act, 1996.
The station was fined €14,000 in court after pleading guilty to the offences of using an unverified instrument and selling short fuel measures.