The log, as a file
Two files. The raw one is exactly what was typed at the pump, 301 tanks and 4 purchase rows. The derived one adds every computed column. Both are rebuilt with the site.
Licensed CC BY 4.0. Use it for anything; say where it came from. Latest tank in the file: Sep 13, 2026.
Raw columns
| Column | Meaning |
|---|---|
| car | Car slug, matches cars.json. |
| date | Fill-up date, local to America/New_York, YYYY-MM-DD. |
| event | fillup, or purchase for the row that marks the day the car was bought (no fuel numbers). |
| odometer | Odometer at the fill, miles. Tracked for the 2023 Corolla only. Its purchase row is 0. |
| miles | Miles driven on the tank being replaced. Trip-meter readings for the earlier cars; odometer differences for the Corolla. |
| gallons | Gallons pumped. |
| cost | Total paid, US dollars. |
| notes | Free text as typed: oil changes, tires, weather, trips. |
Derived columns in fillups.json
| Column | How it is computed |
|---|---|
| ppg | cost / gallons |
| mpg | miles / gallons, blank when the tank has no miles |
| days | days since the previous fill, or since purchase for a car's first tank |
| miles_per_day | miles / days |
| cost_per_mile | cost / miles |
| cum_miles | running total of miles for the car, the odometer for the Corolla |
| temp_mean_f | mean of the daily mean temperatures at the Atlanta grid point from the day after the previous fill through the fill day; blank when fewer than 80% of those days are on record |
| events | tags parsed from the notes: oil, tires, filter, service, trip, weather, premium |
Methods
Averages of per-tank figures (MPG, price per gallon) are means over tanks, which is how the log summarized a year for thirteen years. Overall ratios (miles over gallons, dollars over miles) are shown next to them under their own names, and the two are not interchangeable: a mean of tank MPGs weights every tank the same, the ratio weights big tanks more.
No median, rank or seasonal average is stated from fewer than 5 tanks. A tank under four gallons is never a best or worst tank, because a small top-up produces an unreliable MPG.
Every tank is treated as a fill to full, which is how the log was kept. Dates are civil dates in America/New_York; day counts are calendar differences. No station, location or fuel grade is recorded.
The three earlier cars have no odometer column, so their running mileage is the sum of tank miles since purchase, not a reading. The Corolla's is the odometer.
Weather
Temperatures come from Open-Meteo's historical archive (ERA5 reanalysis), one grid point for Atlanta, chosen as a metro-level reference rather than an address. The daily series is committed to the repository as data/weather-daily.csv (date, mean, max and min in Fahrenheit) and refreshed with a script; days newer than the snapshot are fetched when the site builds, and a tank simply has no temperature when they cannot be. Weather data by Open-Meteo, CC BY 4.0.