The number of U.S. consumers with an auto loan grew 7.8 percent in the fourth quarter, the largest year-over-year increase since TransUnion started tracking the data in 2009.

But nationwide, 60-day delinquencies jumped 6.4 percent to their highest level since 2010, fueled by growing delinquency rates in states with energy-dependent economies.

In the fourth quarter of 2015, 75.6 million consumers had an auto loan, and the average debt per borrower was $17,999, an increase of 3.1 percent over the year-earlier period.

The auto finance market is continuing to grow as sales rise, said Jason Laky, TransUnion senior vice president and auto and consumer lending business leader.

Low interest rates are pushing more consumers to finance their vehicles rather than pay cash. “Growth was observed across all risk tiers, a promising sign for the auto industry as we head into 2016,” he said.

Auto loan and lease originations, which TransUnion reports one quarter behind to ensure all accounts are tallied and included in the data, reached a record 7.5 million during the third quarter, up 8 percent year over year.

TransUnion doesn’t report total auto loan debt, but the Federal Reserve Bank of New York says it’s increasing. Auto debt outstanding rose 12 percent to $1.06 trillion in the fourth quarter, the Fed’s quarterly report on household debt and credit said last week.

While auto debt rose, the share of auto loans 90 days delinquent fell slightly to 3.4 percent, which is less than credit card and student loan delinquency rates, the Fed said.

‘Pockets of pain’

Sixty-day auto delinquency rates climbed, though, according to TransUnion, jumping 6.4 percent to 1.24 percent.

“As lenders’ portfolios rebalance to accommodate the growth in nonprime lending over the past few years, we expect a mild uptick in delinquency,” Laky said.

The number of subprime accounts in the fourth quarter grew 9 percent from a year earlier to 14.3 billion.

“We remain in a low-delinquency environment but have observed pockets of pain in states with large exposure to the energy industry,” Laky said. “Lenders should be mindful of different economic impacts and employment levels in various regions of the U.S.”

North Dakota, for example, saw a 60-day delinquency rate of 0.74 percent in the fourth quarter, a 42 percent surge vs. the year-earlier. Still, North Dakota’s average 60-day delinquency rate is lower than the U.S. average of 1.24 percent. Other energy-focused states’ delinquencies grew around 14 and 15 percent.

“In those particular markets, lenders should look at their portfolios,” Laky said.

But other factors point to economic growth, he added. “They don’t have me too worried about the slight increase in delinquency rates that we’re seeing.”