Dyfed Powys Police confirmed it has received 59 reports of heating-oil thefts in the past five months compared with 15 in 2007.
There have also been reports of thefts in the north-east and the Outer Hebrides, with thieves spurred on by rapidly increasing oil prices.
Rural insurance specialist NFU Mutual is so concerned by the trend it is launching a publicity drive later this month.
“Since the beginning of the year we’ve had 50 claims relating to oil thefts,” an NFU Mutual spokesperson said. “The year before it would have been negligible.
“We have had cases in County Durham, Scotland, Suffolk, Hampshire, Devon, Cornwall and Northern Ireland. We’re just one insurance company, so the overall figure must be a lot bigger.”
The spokesman said most thefts were worth between £300 and £800. The costs to householders could be greater since they may have to tackle damage caused by leaking oil.