The year's sales were driven by a slowly recovering economy, more available credit and the need for consumers and businesses to replace aging cars and trucks.

General Motors Co. posted December U.S. sales growth of 5 percent compared with the year-earlier month, Ford Motor Co. increased sales 2 percent and Chrysler Group LLC's sales rose 10 percent.

Wall Street cheered the results, sending GM and Ford stock to their highest levels since July 2011. GM shares ended 2.4 percent higher at $29.82 and Ford shares were up 2 percent to end at $13.46 on Thursday.

Research and consulting firm Polk said it expects U.S. auto sales to hit 15.3 million vehicles in 2013. GM and Ford both predicted industry sales of more than 15 million vehicles, but Toyota Motor Corp offered a more modest forecast of 14.7 million vehicles.

For the year just ended, U.S. auto sales rose 13.5 percent to nearly 14.5 million new vehicles, the best performance since 2007, according to Reuters calculations.

In the decade prior to 2008 when the recession slowed the industry, U.S. auto sales averaged nearly 17 million vehicles a year.

While last month's auto sales showed little impact of jitters caused by the so-called fiscal cliff - which proved largely averted - automakers expressed worry over the fog of uncertainty still emanating from Washington.

The impact of a payroll tax increase that took effect at the start of the year and the upcoming congressional debate over raising the U.S. debt ceiling may keep some consumers out of the market in 2013, several automakers said.

"It would have been nice if all the open questions had been resolved in the 'fiscal cliff' discussion over the holiday, but clearly they weren't, and that does extend this period of uncertainty from a consumer point of view," Jonathan Browning, head of Volkswagen AG's American unit, told reporters on a conference call.

A 2 percentage-point payroll tax increase will take about $1,000 from the average household budget, said Ford economist Ellen Hughes-Cromwick.

"It is something that we're looking at very carefully, as it will crimp the consumer spending scene somewhat in the months ahead," said Hughes-Cromwick.

Jesse Toprak, analyst with TrueCar.com, said the hit to households would be about the same amount as a down payment on a new vehicle.

"The cheap financing and improved income will make up for that, but that's something we're going to have a keep an eye on," he said.

Hughes-Cromwick said the tax increases for the wealthiest Americans will not greatly affect auto sales, because they tend to purchase new vehicles even if taxes change.

Tom Libby, an analyst at Polk, said continued low interest rates along with an improved housing sector and new product offerings from major automakers will make 2013 a bullish year for the industry.

Detroit's automakers showed December U.S. sales gains of 5 percent, slightly better than analysts' expectations, but not enough to stave off market-share gains by Toyota and Honda Motor Co Ltd.

The two largest Japanese automakers in the U.S. market rebounded from poor showings in 2011 when their inventory was constrained after the Japan earthquake and tsunami.

Toyota reported a 9 percent U.S. sales increase for December, which met analysts' expectations. Honda's December sales rose 26 percent but fell short of analysts' expectations. Honda sales are up 24 percent on the year.

Toyota's 2012 U.S. sales rose about 27 percent, compared with gains of 3.7 percent for GM, 4.7 percent for Ford, and 21 percent for Chrysler.

U.S. MARKET SHARE

GM's U.S. market share is now at its lowest level since at least 1960, and probably at a low not seen since 1930, according to industry journal Ward's Auto.

GM and Ford lost market share in 2012, dented by competition from Toyota and Honda which recovered from 2011 earthquake-related setbacks.

GM's 2012 market share fell to 17.9 percent from 19.6 percent in 2011. Its market share was 23.5 percent in 2007, before the recession. Ford's 2012 market share fell to 15.5 percent from 16.8 percent in 2011.

"We're always concerned about market share - always," said Mark Reuss, GM chief in North America. "But we're not going to give it away like we did in the past and burn the residuals and the brand values in anticipation of the biggest product portfolio launch that we've had in history."

Reuss referred to the years before GM's 2009 bankruptcy and taxpayer bailout, when vehicle production outpaced demand and it layered on incentives to lower prices for consumers.

The F-Series pickup truck from Ford, the top-selling vehicle in North America for more than three decades, had its best sales month in December since August 2007.

The F-Series remained the best-selling vehicle in the United States, with annual sales of 645,316, followed again by the full-size Chevrolet Silverado pickup, at 418,312.

BMW WINS LUXURY CROWN

Most luxury brands had a good year. BMW for the second straight year edged German rival Mercedes-Benz for the U.S. sales crown, followed by Toyota's Lexus and Honda's Acura.

The two U.S. luxury brands both saw sales fall in 2012, with Cadillac down 1.7 percent and Lincoln off 4.1 percent.

Japanese models swept the next four places, with Toyota Camry leading the Honda Accord, Honda Civic and Nissan Altima. Chrysler's Ram pickup placed seventh, followed by Toyota Corolla, Ford Escape and Ford Focus.

Both GM and Ford went into the recession that began in late 2007 - and into 2008 when gasoline prices spiked - overladen with low-mileage big pickup trucks and SUVs.

GM said on Thursday that in 2012 it sold in the U.S. market more than 1 million vehicles that get at least 30 miles per gallon in highway driving. And Ford said that in the year it sold the most small cars since 2001.

Sales of high-profile hybrid and electric vehicles were a mixed bag in 2012. GM's Chevrolet Volt tripled sales to 23,461, but still fell well short of the company's original goal of 40,000 vehicles. Nissan's Leaf was virtually flat, at 9,819.

Toyota maintained its lead in the green-car category, with total Prius sales of 236,659, up 73 percent with the addition of three new Prius derivatives in the past year.

Chrysler easily beat analysts' expectations and had its 33rd consecutive month of year-on-year sales gains. Its annual sales rose 21 percent. Its market share in 2012 rose to 11.4 percent from 10.7 percent in 2011. Chrysler is majority-owned by Italian automaker Fiat SpA.

Sales for South Korea's Hyundai Motor Corp and Kia Motors Co rose 5 percent. Hyundai, the larger of the sister companies, reported full-year U.S. sales of 703,007 vehicles, a company record.

Volkswagen reported a monthly increase of 31.5 percent for its namesake brand and luxury brands Audi and Porsche and a 30 percent gain for the full year.

December sales fell 12 percent for Lincoln, Ford's luxury brand.

Aided heavily by consumer incentives that reduce the price of the vehicles, GM in December dramatically trimmed its inventory of full-size pickup trucks to 80 days of supply from 139 days at the end of November. Most automakers like to have about 80 days of supply of these pickup trucks.

For the overall industry, the pace of annual sales increases has been in the double digits since the market bottomed in 2009, when it hit the worst annual sales rate since World War Two, adjusting for population.