Wet Stock Reconciliation: The Complete Guide for Gas Station Owners
Wet stock reconciliation is the process of comparing physical fuel in your tanks against what the books say should be there. Here is how to do it right and what acceptable variance looks like.
Wet stock reconciliation is the foundation of fuel inventory management. It is the process of comparing the fuel physically in your underground storage tanks (measured by your ATG - automatic tank gauge) against what your books say should be there based on deliveries received and gallons sold. The difference is your variance, and it tells you whether you are losing fuel to theft, delivery shortages, meter drift, or evaporation.
Most gas station owners either skip wet stock reconciliation entirely or do it monthly - both of which are functionally useless. By the time you spot a monthly variance, you have lost 30 days of data and cannot trace the cause. Daily wet stock reconciliation is the standard.
The Daily Wet Stock Reconciliation Process
Every day, for every fuel grade (regular, mid-grade, premium, diesel), you need three numbers:
- Opening book inventory: Yesterday's closing book inventory (or the physical reading at the start of the period)
- Fuel received: Gallons delivered per the bill of lading (BOL) for any deliveries that day
- Fuel sold: Gallons dispensed per POS/dispenser totalizers
The formula:
Closing book inventory = Opening book inventory + deliveries received - gallons sold
Then compare the closing book inventory against the actual ATG reading:
Variance = ATG physical reading - closing book inventory
- Positive variance: More fuel in the tank than the books say (less concerning, but still investigate - possible meter over-read or temperature gain)
- Negative variance: Less fuel in the tank than the books say (this is where money is lost - delivery shortage, theft, leak, or meter under-read)
Acceptable Variance Thresholds
Industry standard thresholds for fuel inventory variance:
- Daily: +/- 0.5% of throughput
- Weekly: +/- 0.75%
- Monthly: +/- 1.0%
For a tank that holds 10,000 gallons and sells 1,000 gallons per day, a 0.5% daily tolerance means 5 gallons. That sounds small, but if the variance is consistently negative - even by 3 gallons per day - that is 90 gallons per month, or roughly $270-$360/month at current fuel costs. Over a year, that is $3,200-$4,300 in unexplained fuel loss from a single tank.
Use our free Wet Stock Variance Calculator to check if your current variance is in range.
Common Causes of Fuel Variance
Delivery Shortages
The most common source of negative variance is receiving fewer gallons than the bill of lading states. This can happen due to temperature differences between the terminal and your site (fuel expands when warm and contracts when cool), meter calibration at the terminal, or outright short delivery.
How to catch it: Take an ATG reading immediately before and after every delivery. The increase should match the BOL within temperature adjustment tolerance. If your ATG shows 7,800 gallons received but the BOL says 8,000, you have a 200-gallon shortfall to dispute. Jobber statement reconciliation catches these discrepancies systematically.
Dispenser Calibration Drift
Fuel dispensers are mechanical devices that drift over time. A dispenser that over-delivers by 0.5% gives away fuel on every transaction. On a pump that dispenses 500 gallons per day, that is 2.5 gallons per day - $7-9/day lost, or $210-270/month from a single pump.
How to catch it: Persistent negative variance on one grade but not others often points to a calibration issue on the dispensers for that grade. State weights-and-measures testing catches gross errors, but subtle drift between inspections is your responsibility to monitor.
Theft
Employee fuel theft (dispensing fuel without recording the sale) and delivery driver theft (shorting deliveries intentionally) are real risks. Internal theft creates sudden or pattern-based variances that daily reconciliation exposes within 24 hours.
Underground Leaks
Persistent, consistent negative variance across all grades that does not correlate with deliveries or dispenser activity may indicate an underground tank or line leak. This is both a financial loss and an environmental compliance emergency. Leak detection systems (ATG alarms) are your first line of defense, but daily reconciliation often catches slow leaks before the alarm threshold is reached.
What Happens Without Wet Stock Reconciliation
Without daily wet stock reconciliation:
- A 200-gallon delivery shortage goes undetected and costs you $600-700
- A slowly drifting dispenser gives away $200/month for years
- Employee theft goes undetected until it scales to thousands
- An underground leak runs for months before environmental regulators catch it - at which point you are liable for remediation costs
- Your fuel COGS on the P&L is wrong, which means your fuel margin is wrong, which means every decision you make based on those numbers is wrong
FuelCFO performs daily fuel inventory reconciliation for every station we serve - by grade, by tank, every day. If you are not doing this, book a free books review and we will show you what your current variance actually looks like.
