When the closing dip doesn't match your book stock, it's tempting to assume theft. Sometimes it is. But fuel goes missing for many ordinary reasons too, and each one leaves a different pattern in your numbers. Knowing the pattern tells you where to look.
1. Recording mistakes
The most common cause of a "loss" is no loss at all, just a wrong number. A meter reading typed with one digit off, test litres that weren't recorded, a delivery entered against the wrong tank, or a dip taken from the wrong row of the calibration chart.
The pattern: a large gap on one day that disappears or reverses the next.
How to catch it: check readings at shift handover, with the outgoing and incoming attendant both confirming the meter. Software that rejects a closing reading lower than the opening one removes a whole class of errors.
2. Temperature changes
Fuel expands when it warms and contracts when it cools. Petrol changes volume by roughly 0.1% for every 1°C, and diesel slightly less. Fuel delivered warm from a tanker and then stored in a cooler underground tank can appear to "shrink" by a noticeable amount.
The pattern: small, seasonal swings that roughly balance out over time.
How to catch it: track variance as a running total over weeks, not single days. If your supplier provides temperature-corrected delivery figures, record those.
3. Evaporation
Petrol is volatile, so a little is lost as vapour during deliveries, storage and refuelling, especially in hot weather. Diesel evaporates far less.
The pattern: a small, steady loss on petrol tanks, larger in summer, with diesel much flatter.
How to catch it: make sure tank caps, seals and vapour recovery equipment are in good order, and compare petrol and diesel variance side by side.
4. Dispenser meters out of calibration
Meters drift over time. If a nozzle dispenses more fuel than it records, you lose stock on every sale without anyone doing anything wrong.
The pattern: a steady loss that grows in line with sales on the tank that nozzle draws from.
How to catch it: run regular pump tests with a certified measure, record the test litres, and keep calibration up to date with your local authority's requirements. Compare variance per tank so you can narrow it to the nozzles involved.
5. Short deliveries
If a tanker discharges less than the invoiced quantity, or some of it goes into the wrong tank, you've paid for fuel you never received.
The pattern: a loss that appears on delivery days.
How to catch it: dip before and after every delivery, let the fuel settle before the "after" dip, and compare the difference with the delivery note before signing. Our guide to accurate tank dips explains the routine.
6. Leaks
A leaking tank, pipe or joint is both a financial loss and an environmental and safety risk. Small leaks can run for months before anyone notices.
The pattern: a steady loss that continues even when sales are low, including overnight when the station is closed.
How to catch it: compare a closing dip with an opening dip the next morning when nothing has been sold. Any drop needs immediate investigation by a qualified contractor. Water in the tank is another warning sign worth checking with water-finding paste.
7. Unrecorded sales and pilferage
Fuel dispensed without being recorded, meters tampered with, or fuel siphoned from tanks. It's the cause everyone worries about, and it's much harder to hide when your numbers are tight.
The pattern: losses concentrated on particular shifts, attendants or nozzles.
How to catch it: reconcile readings and cash every shift, rotate duties, restrict who can edit records, and keep an audit trail of every change. When variance is tracked per shift, patterns stand out quickly.
Reading the patterns together
| What you see | Most likely cause |
|---|---|
| One big gap that reverses next day | Recording or dip error |
| Small swings that cancel out over weeks | Temperature |
| Steady small loss on petrol, worse in summer | Evaporation |
| Loss that rises with sales on one tank | Meter calibration |
| Loss on delivery days | Short delivery |
| Loss even when nothing is sold | Leak |
| Loss tied to certain shifts or staff | Unrecorded sales or pilferage |
The common thread: daily numbers
Every one of these causes is easier to spot when you compare book stock with dips every day, for every tank, and look at the trend. If you only reconcile at month end, a slow leak or a drifting meter has had 30 days to cost you money.
Not sure how to do the comparison? Start with how to calculate fuel stock loss. FuelBotics does it automatically from your readings, deliveries and dips, shows the gain or loss between every dip, and alerts you when it crosses your threshold.
