There have been 21 cases of home fuel thefts in rural areas reported to police in Cumbria this year, Cumbria Constabulary has said.
The thefts, which work out at one every four days, have been valued at about £10,000 by the force.
Police say across the country there has been an 89% rise in fuel thefts since the beginning of the year.
Cockermouth dairy farmer Ian Bowness said rural firms must remain vigilant as thieves see them as "easy pickings".
A recent spike in crude oil prices has seen the cost of heating oil surge, which has led to an increase in tanks at rural homes and businesses being targeted.
The NFU says the price of kerosene, which used as a heating oil, has more than doubled from what it was in October.
Mr Bowness, who is also the chairman of Cumbria NFU, said: "My friend calculated based on what fuel they'd used last year, they were looking at nearly a £20,000 increase in fuel costs.
"The steep rise in price is having a massive impact, and farmers are certainly a more lucrative target, as CCTV becomes more widespread in towns and cities, we've become more of a target as we're rural and we are seen as easy pickings."
Serious and organised crime prevention officer Paul Cavagin, from Cumbria Police, said: "It was predominantly diesel fuel, such as red diesel or white diesel - the stuff you put in your car - that was stolen, but now we're seeing thefts of heating oil which has always been fairly rare, but now are on the increase, unfortunately.
"People have been targeting rural locations, whether it's vehicles, oil tanks, commercial premises or private dwellings and siphoning the fuel off to be sold elsewhere."
Mr Bowness said: "Fuel thieves see rural areas as easy money and while there's no doubt the police are more pro active, absolutely no doubt about that, they have limited resources and there's only so much you can do."
He said farmers should take simple steps to protect themselves, such as securing their premises by installing cameras, improving lighting and closing gates.
"If you can keep them out, it's half the battle," Mr Bowness said.
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