Updated from 12:58 p.m. EDT

Vehicle sales for two of Detroit's automakers skidded last month as aggressive promotions over the summer months led to a dearth of buyers in September.

General Motors ( GM) reported Monday that its U.S. sales fell 24% in September compared with the same month last year, in a continued decline after its "Employee Discount for Everyone" incentive program drove sales in June and July.

The world's largest automaker put its U.S. sales tally at 349,202 vehicles for the month, down from 458,799 last year.

GM's sales rose 41% in June and 20% in July thanks to heavy promotions. In August, it lost momentum, recording a 17% drop-off.

Ford ( F), which ran summer specials of its own, reported a 19% decline in September sales.

Analysts on Wall Street were expecting the No. 2 U.S. automaker to post a decline of roughly 15%. The company sold 228,157 new vehicles during the month. Car sales rose 3%, while truck sales dropped 27%.

With gas costs rising at the pump, traditional sport utilities were hit the worst, and sales slid 51% from September 2004. "A strong showing last year, when the company offered 0 percent financing for 72 months, exacerbated the magnitude of the decline," Ford said.

Sales of crossover utilities shot up 39% in September. The Ford Escape Hybrid set a new monthly sales record with 1,808 vehicles sold. Almost 15,000 Escapes equipped with hybrid engine technology have been sold so far.

On the brighter side, DaimlerChrysler ( DCX) said its U.S. sales rose 4% for the month, with buyers taking 193,108 new vehicles off of dealer lots.

Sales for its Mercedes brand rose 1% to 17,552 vehicles, while its domestic Chrysler unit saw sales increase 4% to 175,556 vehicles.