Auto makers capped a successful year by ringing up strong U.S. sales last month, with General Motors Co. and Fiat Chrysler Automobiles posting double-digit gains. As reported by the Wall Street Journal, Ford Motor Co. also said it enjoyed its strongest December for U.S. sales since 2005, but its growth lagged its competitors.

Observers had projected a robust performance from car makers in December, traditionally a strong month for auto sales. Holiday deals and incentives, along with falling gasoline prices and improvement in the U.S. job market, are among the main factors driving consumers to showrooms.

The question now becomes whether the industry can sustain this kind of growth in 2015. Auto information service Kelley Blue Book said it expects auto makers to sell 16.9 million vehicles in the U.S. this year—the highest sales number in 10 years—indicating more growth, albeit at a slower rate.

“The momentum the economy carried through 2014 accelerated in the fourth quarter,” said Mustafa Mohatarem, who is GM’s chief chief economist. “Car-buying fundamentals remain strong and we expect higher industry sales in 2015.”

GM said much of its 19% sales increase for December came from retail transactions, while combined pickup truck deliveries surged 43% to nearly 87,000 units. Overall, GM said it sold 274,483 vehicles in December, compared with 230,157 a year earlier. The company said it was its best December since 2007.

Ford, meanwhile, sold 220,671 units but posted an increase of only 1.2%. Its full-year sales total was nearly 2.5 million, down slightly from 2013, as the company conducted a changeover for its popular F-150 pickup and performed a planned cut of 15% in daily rental sales.

Ford truck sales rose 4% in December, with the new F-150 becoming the company’s fastest-turning vehicle at dealerships, although overall F-series sales fell slightly for the month. Car sales, meanwhile, declined 1.1%.

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