Fuel Inventory Reconciliation: Why Gallons Seem to Disappear
Every fuel farm keeps two sets of numbers: what the paperwork says should be in the tank, and what's actually there when you measure it. On a good day they nearly match. On a cold morning after a warm delivery, they can be off by dozens of gallons, and nobody took a drop.
Reconciliation is how you tell the difference between a number that moved and fuel that moved.
Book Inventory vs Physical Inventory
The arithmetic is the same at most operations:
- Book inventory is the last measured inventory, plus every gallon received, minus every gallon sold or used.
- Physical inventory is what you measure: a stick reading or a tank gauge, converted to gallons with the tank's strapping chart (the table that turns inches of fuel into gallons for that tank).
- Over or short is physical minus book. Logged every day, it shows a trend that a single reading can't.
Take readings the same way each time, and not while fuel is moving in or out of the tank. A reading taken mid-transfer or mid-delivery doesn't describe any one moment.
Why Temperature Makes a Tank Look Short or Long
Fuel expands as it warms and shrinks as it cools. A stick reading measures volume at the fuel's temperature right now, which the gross vs net post calls gross gallons. Receipts and sales can be measured at very different temperatures.
For Jet A at 43.79 API, AvGrav's correction math puts the effect at about 5 gallons per 10,000 for every degree Fahrenheit. A 20°F swing between a summer delivery and a cool night is about 100 gallons on 10,000.
A Worked Example
Here's one day in a Jet A tank, with that same fuel throughout and no leak at all:
- Opening stick: 4,000 gallons at 65°F.
- Received: 8,000 gross gallons, delivered at 85°F.
- Sold: 6,000 gallons through a meter without temperature correction, with the fuel at 80°F.
- Next morning the tank has cooled to 55°F, and the stick shows 5,934 gallons.
In gross gallons, the book says 4,000 + 8,000 − 6,000 = 6,000. The stick says 5,934. You're 66 gallons short.
Now put every figure into net gallons at 60°F:
| Line | Gross | Net @ 60°F |
|---|---|---|
| Opening, 65°F | 4,000 | 3,990 |
| Received, 85°F | 8,000 | 7,898 |
| Sold, 80°F | 6,000 | 5,939 |
| Book | 6,000 | 5,949 |
| Stick, 55°F | 5,934 | 5,949 |
On a net basis the tank balances. The 66 gallons were never fuel; they were heat that left overnight.
Gross or net, the rule is the same: every figure in one reconciliation goes on the same basis. Mixing a net receipt with a gross stick reading creates a variance out of nothing.
What a Real Variance Looks Like
Temperature effects go both ways and follow the weather. A real loss keeps going no matter what the weather does. Things worth a closer look:
- A shortage that keeps growing in the same direction, day after day, even after temperature is accounted for.
- A sudden jump on one day that a delivery, a transfer, or a temperature change doesn't explain.
- A pattern tied to one truck, meter, or shift, which can point to a meter, a recording habit, or a missed ticket.
- Water on the stick. Record the water reading every day, even when it's zero. Water rising in a tank is a quality problem before it's an inventory one.
How big a variance needs action, and who you report it to, comes from your own procedures, your fuel supplier, and any rules that apply to your tanks. For jet fuel, the airline industry's A4A Specification 123 covers procedures for accounting for jet fuel inventory.
Habits That Keep the Numbers Honest
- Write the temperature and the API gravity next to every gross figure, so it can be corrected later.
- Know which of your meters, if any, are temperature compensated, and don't correct their readings a second time.
- Use the right strapping chart for each tank, and keep it with the tank's records.
- Write down every movement: deliveries, sales, transfers between tanks, defuels, and sumps or samples drained.
Where AvGrav Fits
AvGrav does the gross to net step with the published API tables. Enter the gravity reading and its temperature, then the gallons in Fuel Volume, and it shows Net Volume @ 60°F and the total weight. Each reading saves with a Tank or Truck name, the time, and a note, and History exports today, the last 7 days, or everything as a spreadsheet or a summary PDF for the books. It's a reference tool for the math, not a replacement for your inventory procedures.
If your records and tickets run on Zulu time, AvClock, from the same developer, shows UTC next to local time for any airport, which helps when a reading's timestamp and a delivery's don't line up.
Common Questions
How do you reconcile fuel inventory?
Start with the last measured inventory, add the gallons received, and subtract the gallons sold or used. That's the book inventory. Measure the tank, convert the reading to gallons with its chart, and compare. The difference is the over or short for the period.
Why does my fuel tank show a shortage when nothing leaked?
Often it's temperature. Fuel delivered warm shrinks as it cools in the tank, so a stick reading in gross gallons comes up short against gross receipts. For Jet A, that's about 5 gallons per 10,000 for every degree Fahrenheit.
Should inventory be kept in gross or net gallons?
Follow your own procedures, your fuel supplier, and any rules that apply to your tanks; practice differs. What matters most is that every figure in a reconciliation is on the same basis, and that the basis is written down.
AvGrav and this guide are reference and convenience tools, not certified measurement instruments or a substitute for a calibrated hydrometer, thermometer, or your organization's official procedures. Always follow your organization's quality control program and applicable regulations before accepting, rejecting, or releasing any fuel.