Sales of cars and light duty trucks slipped in May as a result of decreased retail demand and a selling period that was two days shorter than the same period a year ago. The results reflect concerns expressed by analysts and dealers that market growth is cooling despite low interest rates, inexpensive gasoline, sales incentives and increased deliveries to fleet customers.

Among the major automakers, General Motors Co. posted sales of 240,450 vehicles for the month, an 18 percent drop compared to May of last year. GM indicated that deliveries to buyers slipped 13 percent, largely owing to the reduced number of selling days and limited supplies of new vehicles. The company says it has been unable to meet demand for key models, including the Cadillac XT5 and redesigned versions of its pickup trucks, SUVs and sedans.

For its part, Ford reported monthly sales of 234,748 light vehicles, a 6.1 percent decline. While deliveries of Ford F-Series trucks rose 9% and sales of Transit vans were especially strong, overall results for the company were hurt by a 25 percent drop in sales of its passenger cars.

Buoyed by a 14 percent jump in sales of its Jeep brand, Fiat Chrysler Automobiles posted sales of 204,452 vehicles, a 1.1 percent increase over May of 2015. The increase extended FCA’s record of year-over-year gains to 74 straight months. Sales of its Chrysler, Dodge and Fiat brands declined for the month while Ram remained flat.

Elsewhere in the industry, Toyota reported a 9.6 percent decline, Honda posted a drop of 5% and Nissan indicated that its sales were down by 1% for the month.