Chart courtesy of Black Book.

Chart courtesy of Black Book.

The values of sub-compact cars have depreciated an average of 24.2% in a year, which ranked at the top of the vehicle classes tracked by Black Book.

Other top declining categories include compact vans and luxury cars, which depreciated by 23.5% and 23% respectively. Small pickups saw the lowest depreciation in the same amount of time, showing a 8% decrease, according to the Sept. 6 Black Book Market Insights report.

Overall car values depreciated at a rate of 0.75%, which was higher than the average of 0.66% in the last four weeks. Meanwhile, overall truck values decreased by 0.37% last week, similar to its recent average of 0.40%.

"Most car segment values continued to decline at a steeper rate last week," said Anil Goyal, senior vice president of automotive valuation and analytics. "As both credit availability and inventories remain high, Labor Day Weekend should provide a good boost to clearing the inventory."