Dyfed-Powys Police is appealing for witnesses following the theft of fuel from a tank in Llanrhaeadr ym Mochnant.
The offence occurred between 4pm on Thursday and 5pm on Friday and involved diesel taken from a commercial vehicle.
If you have information or saw any suspicious activity please call Dyfed-Powys Police on 101 or Crimestoppers on 0800 555 111.