General Motors said U.S. sales rose nearly 4% in September, boosted by incentives on its pickup trucks, while Ford Motor and ToyotaMotor posted declines.
GM said it sold 337,640 vehicles in the U.S. last month compared to 338,380 vehicles a year earlier.
Sales were adjusted for an extra selling day last September.
Ford Motor said U.S. sales fell 18.3% last month, hit by a decline in showroom sales.
The second-largest U.S. automaker sold 189,893 vehicles in September, down from 204,070 vehicles a year earlier. The percentage decrease in sales is adjusted based on the daily sales rate and reflects 25 selling days in September versus 26 in the same month last year.
Ford said retail, or showroom, sales fell 15%, while sales to car rental companies were down 62%.
Results for Ford, which had sought to cut its lower-margin fleet sales to car rental companies, included its import brands and some medium- and heavy-duty trucks and were not adjusted for extra selling day last year.
Ford, which in the midst of a sweeping restructuring, is aiming to hold its U.S. market share at around 14 to 15 percent.
In the first eight months of 2007, Ford's share was 14.9 percent.
Meanwhile, Toyota Motor said its September U.S. sales slipped 0.6% from a record level of a year earlier.
The Japanese automaker, on track to outpace Ford as the second-largest automaker in the U.S. market, said it sold 213,043 vehicles in September, down from 222,950 vehicles a year earlier.
Chrysler said on Tuesday its U.S. sales fell 5 percent in September as the automaker cut back on sales to daily rental companies.
Chrysler said it sold 159,799 vehicles in the United States last month, compared with 168,888 a year earlier.