Suffolk Police officers have caused almost £10,000 worth of damage to vehicles by using the wrong sort of fuel.
Since April, they have managed to put petrol into a diesel car or vice versa 15 times at a cost of £1,606, a spokeswoman said.
In the past five years officers have made the blunder more than 60 times and the force has forked out £9,127 to repair the vehicles.
In 2006/07 the cost of rectifying vehicles was £2,857 after 19 mistakes were made.
"Unfortunately even police officers and staff are prone to making mistakes such as this and it is down to human error," said a Suffolk Police spokeswoman.
"Suffolk Constabulary's transport services department do all they can to prevent this from occurring. Over the last 36 months, coloured discs labelling what fuel each vehicle takes have been fitted over the fuel caps of every vehicle in our fleet.
"The disc has to be moved out of the way before the fuel cap can be removed and the fuel pump nozzle inserted. While the discs are not foolproof they are a very low-cost preventative measure and have generally been effective in reducing the number of mis-fuelling."
© Press Association 2009