I have the entire gas history for my 6 year old vehicle in excel.
I also have the same logs from my previous three vehicles, going back to 1994.
The numbers that I enter from each fill up are the date, gallons, total cost, and mileage. I calculate everything else. (I write the mileage on the credit card receipt each time I fill up) The good thing Is that I can reformat my output to whichever CSV columns that you are using.