In reply to Cookie (North East Wales MC):
Mostly they give you a full tank and expect you to bring it back full, which is ok in theory but if you are coming south from Benidorm/Calpe there are not many cheap places to fill up on the motorway close enough, even the normal services are a way off Alicante. I guess if you can be bothered to go on the N roads you might find something closer and cheaper. Personally I could never be bothered and just handed the car in after filling up on the motorway, I've never been charged extra for the car not being full if it was reasonable.