Strong May sales lowered U.S. vehicle supplies to a 66-day level on June 1 vs. 79 days on May 1.
Total June 1 stock was 4.15 million units - 75 days of trucks and 56 days of cars.
But while inventories shrank, they were on the high side for this time of year. June 1 stocks were the third highest for the month since 1994. A 60-day supply is considered ideal.
John Casesa, an analyst at Merrill Lynch & Co. in New York, expects supplies to shrink further through the month and forecasts "another strong sales month in June." U.S. sales rose 3.4 percent in May.
Among the Big 3, the Chrysler group had the most significant drop. It fell to a 69-day supply compared with 83 days on May 1. Stocks of Chryslers, Dodges and Jeeps all dropped.
Supplies of General Motors vehicles fell to 77 days on June 1 from 89 days on May 1. GM continued to carry a heavy load of Hummer SUVs. Hummer stocks rose to 115 days from 92 days a month earlier.
Of the Big 3, Ford Motor Co. had the largest supply - 80 days - compared with 91 days on May 1. The heaviest stocks were at Lincoln and Mercury, where large SUV inventories elevated the numbers.
The majority of Japanese automakers entered June with lower days' supplies than the domestics.
American Honda Motor Co. Inc. had only 39 days, Nissan North America Inc. recorded a 62-day supply, and Toyota Motor Co. showed only 36 days of stock.