By Jim Donovan

PHILADELPHIA (CBS) — Do you consider gas mileage when buying a new car? Well, if you bought a Kia or Hyundai over the past few years, what you expected to get in mileage and what you’ll actually get may be two different things. 3 On Your Side Consumer Reporter Jim Donovan finds that both automakers overstated the fuel economy on about 900,000 vehicles.

When Krista and Curtis Haar bought a new Kia, low mileage was a selling point for them. According to Curtis, “Absolutely it was a factor.”

Thus, the Haars were surprised to learn that Hyundai and Kia now say that there was an error when the companies conducted their fuel testing. In fact, the automakers overstated the fuel economy for approximately 35 percent of the 2011-2013 models sold since 2010.

The largest drop in mileage was found for the Kia Soul. Its highway fuel economy estimate will be lowered by six miles a gallon, taking it down to 29 miles per gallon. Fuel economy for the Hyundai Elantra will be reduced by one mile per gallon. The Hyundai Sonata and Kia Optima, which are both mid-sized sedans, were not impacted by the overstated mileage.

Kia and Hyundai say they will pay owners back for additional fuel costs by issuing them debit cards. The debit cards will be issued to owners based on the miles driven and average price of gas, plus an additional 15 percent. Owners can take their car to a dealership and have the odometer checked and the number of miles driven recorded.

For more information, visit: www.hyundaiusa.com/about-hyundai/news/Corporate_2012_HYUNDAI_AND_KIA_INITIATE_VOLUNTARY_PROGRAM-20121102.aspx