Black Book's June Used Vehicle Retention Index that measures wholesale values increased 0.7 to 113 from the May level. The index has declined 4.5% in the past 12 months.

The index is calculated using Black Book’s published wholesale average value on two- to six-year-old used vehicles, as a percentage of original typically-equipped MSRP.

The index rose for the second time in the past three months. It increased slightly in April due to a stronger-than-expected spring selling season, and saw gains in June largely because falling gasoline prices boosted the sale of used trucks, crossovers and SUVs. Despite these gains, the falling gasoline prices also meant a continuation of accelerated depreciation for subcompact and compact cars.

"In addition to falling gas prices, which are playing a role in driving a little more interest for certain trucks today, there are generally some very good deals out there for used vehicles currently," said Anil Goyal, senior vice president of automotive valuation and analytics. "These are the primary reasons why we are seeing some bounce off the lows in used car retention trends."

The index tracks data back to January 2005, which offers a benchmark index value of 100 for the market. During 2008, the index dropped by 14.1% while during 2016, the index fell by just 6.4%. During 2011, the index rose strongly from 113.3 to 123.0 by the end of the year as the economy picked up steam and used vehicle values rose higher. It continued to remain relatively stable, rising slightly until May of 2014 when it hit a peak of 128.1.