Used full-size vans recorded a stout May at auctions, as used vehicle retention value slipped 0.4 percent, following several months of resale strength, according to Black Book's monthly report.

The month recorded only a slight dip, and was better than pre-recession levels of an average of 1-2 percent in monthly depreciation. However, the decline in May signals the start of the slowing summer resale season, said Rick Beggs, Black Book's editorial director.

"As we've seen first-hand from the dealer comments collected by our survey personnel at wholesale auctions, the summer season is kicking in and there is less activity around the car lots," Beggs said. "Many dealers will begin to prepare their inventory strategies for the incoming new model year in a few months, depicting higher depreciation between now and the end of the year."

Full-size passenger vans led all segments by gaining 2.5 percent in value, while full-size cargo vans gained 1.7 percent in May. The vans include the Ford E Series (E-150, E-250, and E-350), Freightliner Sprinter, Dodge Sprinter (2500 and 3500), and GMC G Series (G1500, G2500, and G3500).

In May, compact cars led all car segments with a monthly gain of 0.8 percent in value. These vehicles include the Honda Civic, Toyota Corolla, Chevrolet Cruze, Ford Fiesta, and Ford Focus. The average segment price reached $9,383, a loss in value of 6.8 percent from a year ago.

Luxury cars again led all segments with the highest depreciation, falling 1.5 percent, which was a slight improvement from the segment's 1.8 percent decline in April. These vehicles include the BMW 5 Series, Cadillac DTS, Mercedes-Benz E-Class, and Lexus IS250. The average segment value reached $20,190.

Luxury SUVs recorded the highest depreciation among truck segments, falling 1.0 percent, a modest deterioration from April's 0.8 percent decline. Vehicles in this segment such as the Cadillac Escalade, Mercedes-Benz G Class, and Lincoln Navigator sold for an average price of $32,994.

Outside of their luxury counterparts, four of the top eight segments included full-size pickups, mid-size pickups, full-size SUVs, and mid-size SUVs that rose 0.6 percent, 0.5 percent, 0.2 percent, and 0.1 percent respectively.

Black Book's monthly depreciation report analyzes sales of 2008-2012 model-year vehicles from data collected at vehicle auctions.