In a presentation on Wednesday, Experian said the balance of loans that were 60 days delinquent increased 27 percent, to roughly $4 billion, in the third quarter from the same period a year ago.
Signs of trouble in the market come after a significant increase in lending to people with damaged credit and limited financial means.
Analysts have warned that a loosening of underwriting standards for subprime auto loans could cause widespread losses in the financial system because much of the debt has been securitized and bought by investors around the globe.
Some of the highest delinquency rates in the quarter are concentrated across the South in Mississippi, South Carolina and Alabama. North Dakota had the lowest delinquency rate.
Finance companies, which tend to focus more on subprime customers than traditional banks, had the largest increases in delinquencies in the third quarter