Chrysler announced that Fiat S.p.A.’s ownership interest in the company has increased from 53.3 to 58.5 percent, in accordance to the June 10, 2009 Operating Agreement.

As stipulated by the agreement, Chrysler issued a letter to the U.S. Department of Treasury stating that the company “has irrevocably committed” to begin assembly of a mass-production vehicle with a combined fuel economy of at least 40 mpg in a plant located in the United States.

The model is the 2013 Dodge Dart, Chrysler’s upcoming compact sedan.

“In late December, Chrysler Group achieved the Fuel Economy Test, for an unadjusted combined rating of 40 mpg [5.9 liters per 100km] with a pre-production version of the Dodge Dart, its new, state-of-the-art, four-door sedan,” said the company in a statement.

The key word here is “unadjusted” that refers to the fuel economy measurements for the Corporate Average Fuel Economy [CAFE] and which means the actual combined EPA estimate will most likely not be as high.

Nevertheless, the Fiat Group achieved its goal and its stake in Chrysler increased automatically by 5 percent. As a result, the Italian group now owns 58.5 percent of Chrysler stock with the United Auto Workers (UAW) owning the remaining 41.5 percent.

The Dart will be officially unveiled at the Detroit Motor Show on January 9 and will be manufactured at Chrysler’s Belvidere Assembly Plant in Illinois.