General Motors, Nissan North America and American Honda accounted for most of a 128,100-unit increase in U.S. light vehicle inventory between Sept.1 and Oct. 1.
The three automakers added a combined 94,800 vehicles during September as the industry total grew to 3.1 million units.
The Oct. 1 total is still the third lowest so far this year.
GM started October with an 82-day supply based on September's sales pace, up 18 from Sept. 1. Stocks of the Chevrolet Silverado pickup rose to a 115-day supply from 98, and the GMC Sierra pickup rose to 98 days from 87.
Nissan stocks rose to a 70-day supply from 54.
American Honda added 17 days to reach a 62-day supply.
The industry average was 63 days on Oct. 1, up from 56 days a month earlier.
For the industry, 63 is in the sweet spot of a traditional ideal of 60- to 65-day supply. But Honda normally runs leaner than the industry average.
Looking at individual brands, Land Rover, Subaru and Audi had the lowest stocks, all with less than a 30-day supply.
At the high end, five brands started October near or above 100 days.
Fiat was the highest at 151 days, up from 129.
Mitsubishi was next at 114 days, up from 97. Cadillac and Lincoln tied at 100 days. Volkswagen brand trimmed seven days off its stocks since Sept. 1 but still came in at 97 days.