Most people underestimate the cost of running a car, researchers have found.

It costs around €3,000 a year to run a car, but large numbers of motorists mistakenly believe it costs only €2,000.

Diesel drivers spend the most keeping a car on the road, research from the state-supported Economic and Social Research Institute (ESRI) found.

The cost of a litre of diesel has shot up in recent weeks as the conflict in the Gulf has reignited. It is now more than €2 a litre in most forecourts, higher than petrol prices.

The rise in the cost of fuel forced the Government to recently extend the 30c cut in excise duty on diesel and the 27c cut in the duty on petrol until the end of October.

Motorists around the country say that the rise in diesel prices in the last week had brought the cost of a full tank to more than €100.

ESRI researchers surveyed a nationally representative sample of more than 800 motorists across Ireland.

In the survey, funded by the Department of Transport, drivers were asked to give their best estimate of how much they spent each year on owning and running their car.

They were only then guided through a detailed breakdown of expenses, including fuel or charging, insurance, tax, maintenance, parking, tolls and other costs.

More than seven in 10 motorists underestimated their annual motoring costs — mostly by a big amount.

Underestimation appeared to be the norm across socio-demographic groups and engine types.

Excluding the cost of purchasing the car and depreciation, the median estimate by those surveyed was €2,000 a year.

But the ESRI researchers said actual costs added up to almost €3,000.

“In other words, reported costs were almost 50pc higher than drivers initially believed. Fuel was the largest single reported expense, with a median annual cost of €1,560,” the research body said.

The study found that the costs most likely to be underestimated were less frequent and variable ones such as insurance, maintenance and parking and tolls.

Insurance costs for motorists have stabilised in the past few months, but are still regarded as high.

The findings showed that many drivers overlooked substantial costs when thinking about the financial implications of car ownership, the authors said.

The research also found large differences in costs between vehicle types.

Drivers of electric vehicles reported annual running costs close to half those of drivers of petrol or diesel cars.

The median annual cost for an electric vehicle was €1,560, compared with €2,715 for petrol cars and €3,546 for diesel cars.

Senior research officer at the ESRI, and co-author of the report, Shane Timmons said the degree of cost underestimation was similar across engine types.

He said this showed that misperceptions were not limited to any particular group of motorists. The tendency to underestimate was also widespread across age groups and income levels.

“These findings show that most motorists are not aware of how much their car costs them each year,” Mr Timmons said.

“When people think about motoring costs, they focus on the most visible expenses, especially fuel, but overlook other costs that add up over time.”

He said improving awareness of the full cost of car ownership could help people make more informed transport decisions.

The report said improving the visibility of motoring costs may also complement fiscal and infrastructural measures aimed at supporting moves to get people to shift away from using cars to other forms of transport.