The U.S. launch of the 2011 Hyundai Sonata Hybrid has slipped a month, just enough to preclude buyers from taking advantage of a $1,300 Federal tax credit that expires December 31.

According to Hyundai, the first cars will now reach dealers in January or perhaps later, rather than in early or mid December as it had originally hoped. Spokesman Miles Johnson confirmed the delay to High Gear Media editor Marty Padgett.

The 2011 Sonata Hybrid is expected to be one of the few hybrids that delivers higher gas mileage in highway use than in the city. Hyundai cites statistics showing more than half of U.S. driving time is spent at higher speeds.

Hyundai predicted in June that the hybrid Sonata would achieve U.S. Environmental Protection Agency fuel economy ratings of 36 mpg city, 40 mpg highway.

The eagerly awaited hybrid version of the popular 2011 Sonata was first unveiled at the New York Auto Show in March. It is unique among hybrids in having entirely different front styling than the conventional gasoline car on which it's based. That provides clear exterior identification for buyers who want to show off their green credentials.

To reassure any customers who might have qualms about buying a hybrid-electric vehicle from a manufacturer without a previous history in hybrids, Hyundai said last month it would warranty the car's battery pack for 10 years or 100,000 miles of use.

The 2011 Hyundai Sonata Hybrid is the first mass-market hybrid sold with a lithium-ion battery pack, which is more compact and holds more energy than the older nickel-metal-hydride chemistry used in hybrids from Toyota, Honda, Ford, and General Motors.