MRV,
As the database is frequently changed and has custom fields, there is no way to mass upload. It's possible to override your economy/mileage numbers, but this isn't recommended as you'll have no data to back it up.
I suggest inputting your 100 or so tanks over the course of a week or so. It's certainly been done! To make things easier, certain fields will remember what you chose last time so that you don't have to fill them in again
