Inspectors found seals were broken on the pumps at the Cisco Travel Plaza off Interstate 95 near Exit 1 and at the Cisco Travel Plaza near Exit 6.
Comparing the actual volume of gasoline pumped with the amount indicated on pump gauges, they found each pump shorted customers by as much as one quart for every five gallons, Mr. Irvin said.
Both stations are popular places for people headed to and from Florida because of lower gas prices in Georgia and their proximity to the state line.
Mr. Irvin described the problem at the two stations as possibly "one of the worst we've had recently."
The investigation was ordered after an anonymous tip, and several complaints by customers, he said in a news release.
Inspectors strung yellow rope between the pumps to stop customers from fueling their vehicles.
After each pump was tested, an inspector wound a thin cable around the gas pump handle that locked it to the pump so nobody could use it until the gauges are calibrated correctly.