Tourist buses have been targeted in Kilkenny City in recent months and quantities of diesel stolen.
The latest incident took place outside a well known hotel on the outskirts of the city earlier this week when approximately 300 litres of diesel was emptied.
A garda spokesperson said that there had been a number of similar incidents and warned drivers to take precautions against this opportunist type of crime.
"We would advise drivers to park in well lit areas and to park their bus or vehicle with the diesel cap in against the side of the wall which makes it much more difficult for thieves to gain access to their fuel. There are also alarms that can be fitted," said a garda spokesperson.