The fuel was taken from a tank on a site north of Carsphairn near to Windy Standard sometime between last Wednesday and Friday.
Constable Ian Dunn at Castle Douglas said: “Clearly someone is operating in the area stealing diesel from remote locations. Again a large vehicle must have been used to transport the fuel.
“The site where the fuel was stolen is located almost a 30 minute drive into the forest from the A713 north of Carsphairn. We are seeking the help of those who use the A713 road and want to hear from anyone who may have seen anything suspicious on this road between Wednesday and Friday last week.”
Callers can contact police at Castle Douglas through the 101 number.