Fuel Deposit
A fuel deposit appears under prepaid (full-to-empty) policies. At pickup you are charged for a full tank up front, and the deal is that you return the car as empty as you dare without paying again.
In theory it buys convenience: no need to find a station before drop-off. In practice almost nobody arrives running on vapours, so the fuel left in the tank is money you have handed over for nothing. Some agencies refund the unused portion, many do not.
Whether it is worth it comes down to one question — does the policy refund what you leave behind? If yes, and you have a long final leg that will burn most of the tank, it can be fine. If there is no refund, you are almost always better on full-to-full.
Read the contract wording carefully. "Prepaid fuel, no refund" is the phrase that tells you to politely decline and choose full-to-full instead.
Related terms
Fuel Policy
The rule that decides how much fuel should be in the car at pickup and return — and who pays for the difference.
Full-to-Full
The fairest fuel policy: collect the car with a full tank and return it full, paying only for what you use.
Refuelling Fee
A charge applied when you return the car with less fuel than agreed — often the fuel plus a service fee.