Chevrolet, Malibu

The Malibu bows with an all-four-cylinder engine lineup that significantly boosts fuel economy over the last version. It also gets other gas-saving features, such as active shutters that smooth the airflow at its front end, lower rolling-resistance tires, and lighter-weight materials. It's not as efficient as other roomier mid-size sedans, though.

The base Malibu engine is a 2.5-liter four-cylinder, with 192 hp, mated to a six-speed automatic. The combination is rated by the EPA at 22 miles per gallon city, 34 miles per gallon highway. It's a marked increase for the Malibu, though the current Nissan Altima sets the benchmark with a 38-mpg highway rating.

The Malibu with the turbocharged 2.0-liter four is rated by the EPA at 21 miles per gallon city, 30 miles per gallon highway. The same powertrain is being fitted into vehicles across the GM lineup this year, from the Buick Verano to the Cadillac ATS.

The highest-rated gas mileage in the Malibu lineup will come in the form of the Eco, already on sale. With the highest fuel economy ever for a Malibu, the Eco model uses GM's eAssist technology--a set of lithium-ion batteries and an electric motor that recapture energy from regenerative braking and enable start/stop technology and other fuel-saving measures.

The Malibu Eco is rated by the EPA at 25 miles per gallon city, 37 mpg highway. Lagging the base Altima in gas mileage, the Malibu Eco neatly divides the non-hybrid and hybrid versions of strong-selling sedans like the Sonata (24/35 mpg or 35/40 mpg), and the 2012 Ford Fusion (23/33 mpg and 41/36 mpg), but fades when compared with the new Camry Hybrid's 43/39-mpg rating. GM says the Eco delivers almost 600 miles of range on a tank of gas.