A number of drivers broke down after unwittingly filling up their cars with the wrong fuel at the Asda garage in Llangefni on 21 June.
Asda confirmed the mistake lead to two pumps dispensing diesel instead of unleaded petrol for about 10 minutes.
A spokesman said the isolated incident was caused by "human error".
"We are incredibly sorry for any inconvenience this mistake has caused and urge anyone who thinks they may have been affected to contact us as soon as possible," he said.
The incident affected drivers using two pumps at the petrol station, for about 10 minutes between 13:00 BST and 13:30 on 21 June.
Asda confirmed once the problem was identified the pumps were closed immediately.
A supermarket has apologised after diesel was "accidentally" put in unleaded pumps at a fuel station in Anglesey.