The price of diesel in rural filling stations is, on average, 4p more than in urban areas, a survey showed today.
Cars are becoming an "unaffordable necessity" for many living in rural communities, said the Countryside Alliance, which conducted the survey.
The costliest diesel - at 146.9p a litre - was in Purbeck in Dorset and Ryedale in North Yorkshire.
In contrast, diesel in Birmingham and in Dartford in south east London was "only" 139.7p a litre.
Overall, the alliance found that diesel in rural areas averaged 144p a litre, while in urban areas the average was 140p.
Countryside Alliance executive chairman Barney White-Spunner said: "Not only do people living in rural areas have to drive further to go to work, further to access essential services like schools, doctors and the supermarket, but they have to pay a lot more for their diesel to do so.
"The cost of fuel is a major concern for everyone who lives in the countryside, and cars are fast becoming an unaffordable necessity for many rural families. We urge the Chancellor to help the rural economy get back on its feet and to cut fuel duty in his forthcoming Budget."
The alliance survey follows findings earlier this week that UK motorists pay more in fuel tax than any other drivers in Europe.
And a report by the Centre for Economics and Business Research (CEBR) has said that cutting fuel duty would create thousands of new jobs and could be done at no loss to the Treasury.
Campaign group FairFuelUK met Treasury Minister Chloe Smith this week, armed with the initial findings of the CEBR report. Ms Smith is expected to receive the full report today.
Treasury threats to investigate profiteering, following the 5p-a-litre discount on petrol and diesel prices on some Scottish islands, should be expanded into a full-blown inquiry into fuel pricing across the UK, the AA said.
AA president Edmund King said: "It comes as no surprise that accusations of profiteering are flying around after the 5p rebate was officially passed on to drivers yesterday.
"We predicted this would happen as there is no transparency in wholesale and retail fuel markets, unlike in the USA, Australia and South East Asia."
He added: "Higher oil prices have driven up road fuel prices and diesel prices have suffered even more because of seasonal and supply difficulties.
"The fuel supplier will have been forced to pass those on but whether increases reflect fairly market conditions is something the islanders will simply never know.
"Without transparency, drivers can't see if they are paying a fair price for their fuel. Equally importantly, retailers and fuel suppliers can't show that they are playing it straight."
A Treasury spokesman: "At the Autumn Statement, the Government took more action to help households with motoring costs by freezing fuel duty until August and scrapping a second planned rise altogether.
"This came after our decision to cut fuel duty at Budget 2011, abolish the fuel duty escalator and replace it with a fair fuel stabiliser.
"This support is worth more than £4 billion over two years.
"Petrol and diesel will be an average of 10p per litre cheaper than if we had proceeded with the escalator introduced in 2009. In addition, from this week, motorists in remote islands will benefit from a 5p-a-litre cut in pump prices thanks to the Government's pilot rural fuel rebate scheme.
"The Government has also announced a £165 million package of initiatives to unlock the economic potential of rural areas."