Wet-stock variance: check the innocent causes before you suspect anyone
A tank that does not balance is a question, not an answer. Working through the innocent explanations first protects your staff, your reputation and your chances of finding the real problem.
- LitreIQ
Every forecourt owner knows the sinking feeling: the tank reading does not match what the pumps sold. The first thought is often that someone is stealing. Sometimes that is true. Very often it is not. Fuel is a liquid that expands and contracts, it is measured by instruments that drift, and it is recorded by people working shifts at different times of day. A variance is a signal that something needs checking. It is not, on its own, evidence against anyone.
What a variance actually is
In simple terms, for each tank and period: opening stock plus deliveries, minus litres sold through the pumps, should equal closing stock. The difference between that expected figure and what you actually measure is the variance. A small variance in either direction is normal. The useful questions are whether it is outside your normal range, whether it keeps going in one direction, and whether it lines up with a particular event, shift or pump.
The innocent causes, in the order to check them
1. Temperature
Petrol and diesel expand when warm and contract when cool. Fuel delivered warm from a tanker can measure as fewer litres once it cools in an underground tank, and the reverse can happen too. Day-to-day and seasonal temperature changes can therefore move your book figures without a single litre going missing. Where your tank gauge reports temperature-corrected volumes, compare like with like: corrected with corrected, uncorrected with uncorrected.
2. Timing of dips and deliveries
If a tank is dipped at 06:00 but the shift's sales are cut at 06:30, or a delivery is booked on one day but dropped after the closing dip, the numbers will not agree even though nothing is wrong. Check the exact times of the dip, the shift close and the delivery against each other before looking at anything else. Timing errors tend to reverse the next day: a loss today and a matching gain tomorrow is a strong hint.
3. Delivery quantities
Compare the litres on the delivery note with the rise in the tank, measured before and after the drop, with enough settling time. A shortfall here is a delivery question to raise with your supplier, not a forecourt staff question.
4. Pump calibration
A pump that dispenses slightly more than it records gives fuel away on every fill; one that dispenses less is a customer and compliance problem. If variance concentrates on the tank feeding one pump, or one nozzle, arrange a calibration check through your approved contractor. Never adjust dispenser metrology yourself.
5. Water ingress
Water in a tank displaces fuel and can make your stock appear higher or lower depending on how it is measured. Check water readings on your gauge or with water-finding paste on a manual dip. Rising water after rain points to a seal or fill-point problem that needs attention for product quality as well as stock accuracy.
6. Sensor and dip error
Tank gauges and probes can drift, stick or fail, and manual dips depend on the dip stick, the tank chart and the person reading them. A sudden jump that does not match any sales or delivery activity is more likely to be a measurement problem than a real loss. Compare the gauge with a careful manual dip, and confirm the tank chart is the right one for that tank.
7. Legitimate refunds, tests and transfers
Calibration test draws returned to the tank, approved refunds, fuel used on site and transfers between tanks all need to be recorded. If they are not, they show up as variance. Check the records before drawing conclusions.
Think in tolerances, not single days
Decide, with your contractor and your own history, what normal variance looks like for each tank as a share of throughput. Then watch the trend rather than one bad day. A variance that stays inside your tolerance and swings both ways is usually noise. A variance that keeps moving in one direction, outside your tolerance, or that lines up with one shift, one pump or one delivery, deserves a closer look.
Investigation, not accusation
If the innocent causes have been checked and a pattern remains, it is reasonable to look at people and processes. Even then, a variance is evidence that something happened, not proof of who did it. South African labour law requires a fair reason and a fair procedure before disciplinary action. In practice that means:
- collecting the evidence first: readings, times, shift rosters, pump and till records;
- writing down which innocent causes you checked and what you found;
- giving the employee a genuine chance to respond before any decision;
- taking advice from your labour adviser before acting.
Treating every variance as theft damages trust, and it can lead to unfair dismissal claims when the cause later turns out to be a sensor or a tank chart.
How LitreIQ helps
LitreIQ compares tank movement with pump litres, sales and deliveries from the reports you already receive, read-only. When a tank moves outside its tolerance, it opens a case that shows the Rand exposure, the source readings and the likely causes, with the innocent ones listed first and the checks to rule each one out. Every amount is calculated by fixed rules you can trace back to the source data. The case records who checked what, and when, so your investigation is documented and fair.
See it on your own tanks
To see how your tanks behave, start a free 14-day trial on one site, or request a free Profit Protection check and we will look at your wet-stock reports with you.