In a statement Wednesday, the company said the stations in Boise, Nampa and Meridian had a mix of diesel and gasoline in their unleaded tanks.
The problem was discovered Monday after a local mechanic had several cars towed in and learned they had all filled up at the same station.
Jackson Food Stores officials say it appears a fuel delivery driver mistakenly mixed the diesel into the wrong tanks. They say the tanks have been flushed and replaced with good product and the company will cover the repair bills.
Rudy Garza of Meridian was one of the motorists who filled up with the bad gas, and ended up in an auto repair shop with a $2,000 bill.
He says Jacksons corporate offices told him they'd pay the bill.
"Everybody's been real nice so far," Garza told KBOI News. "Obviously when all is said and done, I just want the bill paid and my car running properly like it was before."
In its statement, the company said, "Our investigation surfaced several instances of human errors that led to the issue, and we are changing our policy and procedures to help ensure this doesn't happen again. We take concerns about the quality of our fuel very seriously. We are committed to taking care of any and all customers impacted.
"Of more than 70 locations in the Treasure Valley, we believe the issue is isolated to only four locations. Customers that have purchased fuel at these stores during these times and experienced issues with their vehicle are asked to contact Jacksons Corporate Office at (208) 888-6061."
These are the four Jacksons locations where the tainted gas was sold:
612 Northside Blvd, Nampa (Friday morning)
2728 Orchard St, Boise (Sunday morning)
4315 Garrity Blvd, Nampa (Sunday morning)
1950 E Fairview, Meridian (Sunday morning)
Kevin Merritt with the Department of Agriculture's Bureau of Weights and Measures says the tanks have been tested and are now fine.