Kent Police has been forced to pay more than £25,000 to fix cars after officers filled them with the wrong type of fuel.
The county's force was the second biggest culprit in the UK, racking up £25,629 in repair costs caused by mis-fuelling since 2011.
Figures obtained by Auto Express reveal Kent came second only to the Met Police, which paid out an astronomical £167,118 to rectify damage.
Across the UK, forces have spent almost £400,000 following 2,100 embarrassing mishaps - more than one incident per day.
With an average repair cost of £181.68 for every incident, it has costs the police forces a total of £390,061, according to the data released under the Freedom of Information Act.
But Kent Police says the number of incidents in the county is falling.
"It's an annoying and avoidable mistake that will place an extra burden on stretched resources" - Luke Bosdet, AA
A spokesman said: "Since 2011 the number of incidents of putting the wrong fuel in a fleet vehicle has decreased by just under 66 per cent from 35 incidents in 2011 to 12 in 2015 with the repair costs following in a decreasing trend in 2011 at £8,354 compared with £2,336 in 2015.
"Kent Police has worked hard to support and educate officers and have maximised the use of 'anti-mis-fuelling' devices, many of which have since been fitted by vehicle manufacturers as standard equipment.
"This is a much improved position, however we continue to work with our officers and apply best practice to further reduce unnecessary costs."
Luke Bosdet, a spokesman for the AA, said: "It's an annoying and avoidable mistake that will take a vehicle off the road and place an extra burden on stretched resources.
"But it shows that police officers are human like the rest of us. Stress and pre-occupied minds are often the cause of misfuelling mistakes, which fleet managers can try to beat with fuel-tank labelling and reminders."