While we’re waiting for General Motors to release its December 2012 sales later today, the Detroit-based company found the time to announce that it became the first U.S. automaker to sell more than 1 million vehicles with an EPA-estimated 30mpg (equal to 7.8lt/100km and 36mpg UK) or better on the highway test cycle in its home market in the previous year.

“Our investments in advanced powertrains are clearly paying off, and our smaller vehicles are resonating with customers,” said Mark Reuss, president of GM North America.

“In 2013, we’ll introduce new diesel, eAssist and plug-in vehicles in the United States and expand the availability of turbocharged four-cylinder engines. This will give us the most technologically diverse range of fuel-efficient cars and crossovers in the industry,” he added.

GM says it has 13 vehicles in its U.S. range that either hit or surpass the 30mpg highway threshold including four Chevrolet models, three from Buick, and one from Cadillac and GMC.

The Detroit carmaker added that it expects combined 2012 sales of its mini, small and compact cars to be up about 39 percent, and that around 40 percent of its vehicles by sales volume are powered by four-cylinder engines, 10 percentage points higher than in 2010.