Figures which show Lancashire County Council spends more on staff mileage expenses than any other authority are out of date, the council has claimed.
The authority paid out £8.8m last year to reimburse workers who used their own cars, claimed the Taxpayers' Alliance.
The pressure group said it also gave the highest rate, up to 65p a mile. The average UK rate was 56.4p in 2010-11.
However, current estimates suggest the council will save £2.5m on car travel in 2011-12, the authority said.
The Taxpayers' Alliance survey ranked the Conservative-run council Lancashire alongside Derbyshire, Cornwall and Warwickshire as among those offering the top mileage.
According to pressure group, the figures meant that the typical council worker would have ended up £164 better off for every 1,000 miles driven.
Alliance director Matthew Sinclair said: "Ordinary motorists who are feeling the pinch will be shocked that council staff are getting such a generous deal for their mileage claims. It simply isn't fair.
"Some authorities have shown that it is possible to save millions by cutting back to the rate recommended by the taxman."
Last year, the HM Revenue and Customs-approved level for mileage payments was 40p a mile.
In a statement, county treasurer Gill Kilpatrick said: "These figures are out of date and don't reflect the current position here in Lancashire, where we will save £2.5m on car travel in the current year.
"However, it won't come as a huge surprise that we should be around the top of the table, as one of the largest authorities in the country with 40,000 staff serving 1.2 million residents across a large geographical area.
"It is important to note that these expenses are incurred by staff who deliver a wide range of valuable services to our residents, including visiting vulnerable children and adults in their homes, supporting schools and maintaining our roads.
"We are continuing to try to drive down costs through a range of measures, including making more efficient use of our buildings and tele-conferencing, but our staff will always play a key role out in the heart of our communities."
The council did not reveal its current average mileage payment.
The pressure group's survey found local authorities paid staff a total of £427m in mileage allowances last year. In 2008-09 the figure was £402m.