I use
www.fuelly.com,
www.fuelecononomy.gov, this site, my Google Drive spreadsheet, and I photograph my results at the pump to record them- no more searching for paper or stacks of receipts.
Many record different things, I record my:
Gallons Pumped
Price Paid for MY fuel
Prices for each grade, since I SHOULD use 87 but use 93
Time driving
What my ODO thinks I traveled
What my car computer thinks I got (MPG)
What my SCii things I got (MPG)
And any notes I may have. I don't always use all of it, but in the future, I may want to use more data, or make more connections, or whatever, and it doesn't take but a moment to record it now- and it could be invaluable to me later. Others are more detail oriented, with notes while they drive, specific percentages on highway/city, temperature, and more. It's all about what you want! If pen and paper, gallons and miles works for you, thats what matters!
I do support using multiple fuel trackers, as each one has at least one thing special about it- not one site is
the best or all inclusive.