Fuel sits in tanks underground where you cannot see it, so a station needs a way to know what is down there at all times. That is the job of the automatic tank gauge. It turns a buried tank into a live, recorded number, and it sits at the center of both inventory and leak detection. This guide covers how it works and why it matters.
What an ATG is
An automatic tank gauge is an electronic system that continuously monitors an underground fuel tank. A probe in the tank measures fuel level, water, and temperature, and a console reads it out, tracks inventory, and runs leak-detection tests. It replaces the old manual stick reading with a constant, logged picture of the tank.
How it works
A probe inside the tank senses the fuel and water levels (commonly with a float or magnetostrictive sensor) along with temperature. The console converts those readings into gallons, records them over time, and can run automated leak tests during quiet hours when fuel is not moving. Instead of an occasional dip, you get a continuous measurement.
What it measures
- Fuel volume. How many gallons are in the tank right now.
- Water level. Water at the tank bottom, a problem to catch early.
- Temperature. Needed to correct volume, since fuel expands and contracts.
Its role in compliance
The ATG is usually the heart of a station's leak detection. EPA underground storage tank rules require release detection, and the ATG console runs the automated tests and keeps the records that prove it. Under those same rules, its electronic and mechanical parts have to be tested periodically to confirm they still work.
ATG and wet stock
The ATG and wet stock reconciliation are a team. The ATG measures what is physically in the tank; reconciliation compares that against what your books say you bought and sold. The gauge gives you a trustworthy reading, and reconciliation turns it into an early warning when the numbers drift apart.
Where FastDragon fits
A live tank reading only pays off if it flows into your books and gets compared to your sales. FastDragon brings tank and sales data together so a variance surfaces while it is still small, turning the ATG's numbers into action instead of just a console on the wall.
Questions we hear a lot
Who makes ATG systems?
The consoles most stations run are Veeder-Root's TLS series, OPW's SiteSentinel, and Franklin Fueling's EVO line. Back-office and tank-monitoring software can poll any of the major consoles, so the brand matters less than keeping the probes and sensors tested.
What leak rate does an ATG have to detect?
EPA's monthly monitoring standard for underground tanks requires detecting a leak of 0.2 gallons per hour. An ATG meets it with in-tank static tests or continuous statistical leak detection. The tighter 0.1 gallon-per-hour tightness test is a separate procedure used in specific situations.
Do ATG readings replace stick readings?
Mostly. The probe is the daily source of truth, and it never forgets to take a reading. Many operators still stick tanks now and then to cross-check the probe, and some state inspectors ask for manual reconciliation records, so the gauge stick has not fully retired.
Why does the water reading matter?
Water settles under the fuel, where it corrodes steel tanks, feeds microbial growth in diesel, and in ethanol blends can cause phase separation that ruins the product. A rising water reading can also mean a breach letting groundwater in, so it deserves the same attention as the gallons.