FORT LAUDERDALE, Fla. — AutoNation reported new-vehicle sales for December 2015 of 35,962 units, a 9% increase from the same period one year ago. The nation’s largest publicly traded dealer group said the increase was driven by significant retail discounts offered by manufactures, particularly in the premium luxury segment.

Despite the sales increase, AutoNation officials said the group expects to report a $250 to $350 drop in gross profit per vehicle retailed in the fourth quarter compared to last year.

“The fourth quarter industry sales environment was more push versus pull. As a consequence, we expect to report significant margin declines for the fourth quarter in both our new and used retail unit sales,” said Mike Jackson, the group’s chairman, CEO and president. “We have begun, and will continue through the first quarter, to take necessary steps to align our costs, inventory, and pricing strategy to adjust to the current market. In 2016, we expect industry new-vehicle unit sales will continue to exceed 17 million.”

On a same-store basis, retail new-vehicle unit sales last month increased 5% compared to December 2014. Sales were up 16%, 9%, and 2% for domestic, import, and premium luxury, respectively, on a year-over-year basis.

For the fourth quarter, vehicle sales were up 6% compared to the fourth quarter 2014. Vehicle sales were up 10%, 4%, and 4% for domestic, import, and premium luxury, respectively, on a year-over-year basis.

On a same-store basis, new-vehicle sales in the fourth quarter 2015 increased 3% compared to last year.

For the full year, the dealer group posted a 7% increase compared to 2014, with domestic vehicle sales was up 10%, imports up 3%, and premium luxury sales up 14% compared to 2014.

On a same-store basis, new-vehicle sales in 2015 increased 5% compared to 2014.