Dodge remains Chrysler’s top-selling brand as the auto maker heads into 2012, a decisive year for its partnership with Fiat.

Hard-charging Jeep and promising results from Chrysler’s core brand combined to help the auto maker finish 2011 with a 37.5% December sales jump in the U.S., compared with like-2010, according to WardsAuto data. The performance contributed to a full-year gain of 26.1%.

Chrysler also lays claim to a market-share uptick of 1.3 points, its largest such hike since 2005.

Dodge accounted for 451,040 light-vehicle sales in 2011, a full third of Chrysler’s 1,361,685 deliveries and a 140,000-unit boost over the brand’s 2010 tally.

A 38.3% jump in Dodge light-truck deliveries offset flat sales of its car lines, according to WardsAuto data. But that picture is expected to change this year with the launch of the new-for-’13 Dodge Dart C-car, the first Chrysler product to take full advantage of the auto maker’s partnership with Fiat and corresponding access to Fiat technology.

Except for the Charger fullsize sedan, all Dodge models still in production finished 2011 in positive sales territory, compared with 2010. The Charger’s 7.0% full-year slump contrasts sharply with its strong showing in December, when dealers sold 7,211 units – more than three times like-2010’s total.

The Caravan minivan’s 110,862 deliveries accounted for the most volume of any Dodge model.

Despite a 2009 restructuring that established Ram as its own brand and stripped Dodge of pickup-truck volume, Dodge was Chrysler’s top-selling brand in 2010. But its margin of victory over second-place Jeep was some 69,000 units wider.

Jeep finished 2011 with 419,349 vehicle sales, a 44.0% leap from prior-year, largely because of strong demand for the Grand Cherokee and Wrangler.

The midsize SUVs accounted for delivery totals of 127,744 and 122,460, respectively. Only the Ram pickup, Chrysler’s perennial volume flagship, recorded more sales with 250,181.

Ram-brand full-year sales climbed 26.1%. Chrysler car sales soared 66.1%, with the midsize 200’s 87,033 deliveries accounting for nearly 70% of volume.

Chrysler-brand light trucks marked the auto maker’s only segment to finish the year in negative sales territory, down 21.4% on a surprising 16% plunge in Town & Country minivan deliveries.

The Town & Country was the U.S. market’s best-selling minivan in 2010.

Reid Bigland, Dodge-brand president and CEO and Chrysler’s U.S. sales chief, touts the auto maker’s 45% retail sales hike in December and declares 2011 a success.

“Looking back, we were the fastest-growing auto maker in the country, increasing our market share 2.3 percentage points during 2011,” he says in a statement.

In an earlier email to employees, CEO Sergio Marchionne also celebrates Chrysler’s achievements, such as its repayment of government loans that helped vault the auto maker from its 2009 bankruptcy. And the Dart’s unveiling next week at the Detroit auto show promises greater returns.

“It will be the first Chrysler Group vehicle to feature a Fiat-derived architecture, adapted from the award-winning Alfa Romeo Giulietta,” he writes. “Platform-sharing between Fiat and Chrysler will be a key driver of our efforts to increase efficiencies and volumes in the years ahead.”

But Marchionne also sounds a cautionary note.

“What’s past is prologue,” he says. “As we begin 2012, uncertain global economic forces pose challenges to the entire industrial sector. And in a rapidly changing world, this year will inevitably bring other risks and opportunities not yet foreseeable.”