FRAUDSTERS have ripped off a chain of filling stations by exploiting a flaw in a pre-paid card system for buying fuel.
The gang is targeting stations in Dublin and the commuter belt counties.
And some outlets were hit several times at night before the scam was discovered.
Fuel debit cards can be bought over the counter without having to provide any identification to the retailer.
The gang became aware of the flaw in the system, which allows even card holders with only €1 in credit to buy fuel worth €100.
Now the gang is being investigated by gardai under Operation Acer, which was set up a year ago to tackle criminals responsible for a spate of burglaries and thefts in the greater Dublin area.
Acer feeds into Operation Fiacla, the nationwide crackdown on gangs.
One garda officer said last night: "We are still establishing the full extent of the scam, but we know that the gang has struck dozens of times.
"They focus on stations owned by a major chain and using the pre-paid debit card system.
"The card can be bought for €20. Once it has €1 in credit, it can be used to open a pump and the motorist can obtain up to €100 worth of fuel before the pump automatically shuts down.
"They know the vulnerability of the system and are exploiting it as quickly as they can.
"It was introduced as a facility for the customer, but quick-thinking criminals have turned it to their advantage."
At least one filling station has been shut down while changes are made to the system.
Gardai believe the gang members are Eastern Europeans and have been operating the fraud since the start of the year.
However, it only came to light in the past couple of weeks.
Officers are checking CCTV footage from the forecourts of the stations in an effort to identify the vehicles being used by the fraudsters.
Meanwhile, station owners are reviewing the pre-paid system to eliminate the flaw.