The kilometre options indicate the total number of kilometres that a renter can perform during the rental period. There are three different options: 100km/day, 200km/day and unlimited kilometres.
For instance, for a 3-day hire :
You are free to drive more kilometres in a day, as long as you do not exceed the option you have chosen overall. If you go over the option, extra kilometres will be paid to the owner at the price/kilometre they have set (€0,20/kilometre on average)
For a 3 day hire with the option of 100 km/day, if you end up driving 400km (instead of the 300 initially planned), you will pay : (400-300)*0,2= €20