DANVILLE, Ind. -- Three gasoline stations in Hendricks County are offering refunds to customers who paid more than $4 a gallon there last week, the state attorney general's office said.

The office began investigating the stations -- a Speedway and a Marathon in Danville and a Marathon in Avon -- after receiving complaints that they were selling regular unleaded gas for $4.099 late Friday morning and part of Friday afternoon.

Other stations in the area were selling for about $3.399 per gallon. Attorney General Steve Carter said the investigation revealed that a worker at the Danville Speedway mistakenly set the regular unleaded price at the level for diesel.

Workers at the two Marathon stations learned of the Speedway price and decided to match it, the state said.

"These prices stuck out like a sore thumb and were clearly excessive in the marketplace," Carter said.

After a few hours, the stations lowered their regular unleaded prices to below $3.45 a gallon.

People who bought gas at the higher price will be refunded the difference between what they paid and market price at the time. The difference will amount to about 70 cents a gallon.

"The stations involved have cooperated with our inquiry and recognize the need to provide customer refunds," Carter said.

For the 22 people who bought the overpriced gas at the Speedway station, refunds already have been placed on their credit cards. The 17 Speedway customers who bought the overpriced gas with cash must call 800-643-1948 to receive their refunds, Call 6 for Help's Rafael Sanchez reported.

The Speedway station said any money not claimed within two weeks will be donated to charity.

The Marathon station in Danville already has made its refunds. People who bought the overpriced gas at the Avon Marathon station will need to present their receipt or record of credit card purchase to the station in person, Sanchez reported.

A spokeswoman for Marathon Petroleum, which owns Speedway stations, said the company wants "to offer our apologizes to any customer who was affected by the erroneous pricing."

In recent months, Indiana's gas prices have gone from being below the national average to consistently being about 20 cents above the national average.

Excessive gas pricing can be reported to the attorney general's hot line at 866-241-9753.