PIERRE, S.D. (AP) ‚ÄĒ Two South Dakota companies have been charged in Beadle County with selling 85-octane gasoline mislabeled as higher octane fuel, the result of a state investigation.

Complaints filed Friday charge Rapid City distributor and retailer M.G. Oil Co. with illegally selling 85-octane gasoline and mislabeling the gasoline sold at its five Corner Pantry stations in Huron, Beadle County State's Attorney Michael Moore said Monday. He also said 281 Travel Center in Wolsey has been charged with mislabeling the gasoline it bought from M.G. Oil.

The charges are Class 2 misdemeanors carrying a maximum penalty of a $500 fine and 30 days in jail. Representatives of M.G. Oil and 281 Travel Center did not immediately return phone calls seeking comment.

Moore said the charges were filed against the companies, not the owners. He said he believes the charges are the first in South Dakota as the result of a state investigation that found 85-octane gasoline was being sold while labeled as 87-octane fuel in eight counties.

The prosecutor said 85-octane gasoline cannot legally be sold in Beadle County, and it's illegal to mislabel gasoline at the pump.

"The people that were doing it need to be held responsible," Moore told The Associated Press.

During the investigation, the state Public Safety Department earlier this year also discovered that state law technically prohibited the sale of 85-octane gasoline. Most car manufacturers recommend that gasoline used in their vehicles have a minimum octane rating of 87.

The department, with Gov. Dennis Daugaard's backing, passed an emergency rule making 85-octane gasoline legal anywhere in South Dakota until Oct. 7 to avoid a possible fuel shortage in western South Dakota, where the low-octane fuel meant for higher elevations has been sold for decades.

A new rule allows the sale of 85-octane gasoline only in nine western counties and only until June 30. That means the 2013 South Dakota Legislature will decide whether to permit the sale of the lower octane fuel past next June.

Moore said the rules passed to allow the sale of 85-octane gas in western counties does not affect the allegations that substandard gasoline was being mislabeled and sold in Beadle County in March.