Black Book's Used Vehicle Retention Index for July remains unchanged from June at  a value of 113. The index has now moved positive or unchanged in three of the last four months.

Full-size cars, full-size pickups, luxury cars, and near-luxury cars saw noticeable gains in their respective segment indexes during July. Pickups remain popular because of the price of gas and overall supply in the market, while each of these car segments offer decent value currently, resulting from several months of sharp valuation declines over the last few years.

"What we're experiencing over the last few months are signs of a resilient used vehicle market, where the bottom is not dropping out as some had expected this year,” said Anil Goyal, Black Book's senior vice president of automotive valuation and analytics. "We're paying close attention to several car segments, in particular, compact car and mid-size car which continue to weaken as demand remains soft and used supplies build. In addition, the overall economy and credit availability conditions will influence the retention strength moving forward."

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 dates back to January 2005, where Black Book published 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 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.