March 15 (Reuters) - Model year 2012 passenger vehicles sold in the United States had an average fuel economy rating of 23.8 miles per gallon, the highest on record, the U.S. Environmental Protection Agency said on Friday. Last year's models showed a 1.4 mpg improvement over 2011, the biggest annual improvement since the EPA began keeping records on fuel economy. Improving fuel economy is a key component of the Obama administration's effort to cut U.S. oil consumption and polluting greenhouse gases, which cause global warming. Model year 2012 cars and light-duty trucks sold in the United States average emissions of 374 grams of carbon dioxide, down from 398 grams per mile in the previous model year, the EPA report said. Carbon dioxide accounts for the lion's share of greenhouse gas emissions globally. The EPA said the figures released in its report, which can be seen atare preliminary. Among major manufacturers, Honda Motor Co showed the highest average fuel economy of 26.4 mpg, followed by Volkswagen AG at 26.2 mpg, Mazda Motor Corp and at 25.9 mpg. Among U.S. automakers, Ford Motor Co vehicles reported the best average fuel economy at 23.2 mpg, up from 21.1 mpg for its 2011 models, the EPA said. Hyundai Motor Co would have the highest for 2012 vehicles, at 28.8 mpg, but its figures are under investigation by the EPA. In November, the EPA announced that it was investigating Hyundai and its corporate sister Kia Motors Corp after its own tests showed less performance than what the automakers claimed. U.S. automakers have more pickup trucks and large sport utility vehicles in their lineups, which increases their corporate average fuel economy (CAFE) ratings. Auto manufacturers have increased the number of hybrid gasoline-electric vehicles, plug-in vehicles as well as increased fuel economy for internal combustion gasoline engines in recent years, largely spurred on fuel economy targets set by the Obama administration. In 2011, Obama reached a deal with major automakers that fuel economy for each manufacturer will rise to an average of 54.5 mpg by 2025. By model year 2016, U.S. cars and light-duty trucks by each manufacturer are to average 35.5 mpg. The EPA said the longer term trend of improving fuel economy ratings began with the 2005 model year, during the Bush administration. Since the 2007 model year, U.S. passenger vehicles have shown a 13-percent increase in fuel economy ratings and a 16 percent reduction in carbon dioxide emissions.