The industry had a 58-day supply of cars and light trucks as of Sept. 1, up from 57 days a month earlier.
Total car inventory remained unchanged at 50 days. Truck inventory was at 66 days on Sept. 1, up from 64 days on Aug. 1.
This four-month trend had been expected because automakers have kept a tight rein on production because of soft sales. In addition, days' supply also is lower at this time of year because of vacation shutdowns and model changeovers.
DaimlerChrysler had the largest increase in days' supply of the Big 3: 71 days on Sept. 1, up from 57 days on Aug. 1. Ford Motor Co. and General Motors, on the other hand, barely budged.
GM had a 68-day supply on Sept. 1, up from a 66-day supply on Aug. 1. Ford's 65-day supply on Sept. 1 was up from 64 days a month earlier.
The TrailBlazer, Chevy's new sport-utility, experienced a notable increase to an 84-day supply on Sept. 1, up from a 52-day supply on Aug. 1.
Volkswagen, which has not felt the same sales crunch this year as the domestic makers, had a 47-day supply on Sept. 1, down from a 49-day supply a month earlier.
Toyota Motor Sales also has low inventory based on strong sales. Toyota had a 28-day supply on Sept. 1, down from 36 days a month earlier.