Wholesale used-vehicle prices normally move up a little in September, but Cox Automotive data show that high fuel prices have put a dent on values.

The company’s Manheim Used Vehicle Value Index reading was about 206 for the month, adjusted for mix, mileage and season. That’s down six-tenths of a percentage point year-over-year and 1% from August, when September values normally see a small bump.

The decline in values follows a strong start to the year for used units with greater appreciation than usual for the first half. That eroded, though, as the war in the Middle East inflated gas and diesel prices, the latter to record highs, and interest rates climbed, according to the report.

“Diesel represents a small share of all units on the ground — just over 3% — but we’re seeing a clear downward effect on valuations as diesel prices hit all-time highs, and days’ supply for those vehicles is rapidly rising,” Cox Chief Economist Jeremy Robb said.

Further dampening used-vehicle values is this year's unusual East Coast hurricane season, with a September devoid of hurricanes for the first time in decades, the report pointed out. The damaging storms typically increase used-vehicle demand, but without them depreciation was on the rise.

Electric vehicles, meanwhile, have been a hot item, their days’ supply down as consumers hunt for more fuel-efficient vehicles, Cox said. EV prices were up 4% year-over-year. Compact car prices rose by about the same amount. Non-EV prices, by contrast, fell nearly 2%.