The 2011 Honda Civic GX

The Honda Civic GX is the greenest car of 2011, according to the American Council for an Energy-Efficient Economy.

The nonprofit organization released its 14th annual environmental ratings list yesterday with the Honda Civic GX, which runs on compressed natural gas, once again winning first place. The ACEEE ranked the all-electric Nissan Leaf second, with the Smart Fortwo in third, and the Toyota Prius in fourth. The all-electric Chevy Volt was ranked last at No. 12.

However, topping the ACEEE's list doesn't necessarily mean the Honda Civic GX is the most consumer-friendly green car available. The car, which has been ranked first place for seven years now, runs on compressed natural gas (CNG), making it extremely clean, but it does require the installation of a CNG home-filling station, or locally available CNG filling stations.

One might want to consider the ACEEE's greenest list as more of an industry-focused report card of sustainability rather than an actual car consumer guide like the Fuel Economy Guide 2011 produced by the Environmental Protection Agency and Department of Energy.

Whereas the EPA guide grades mainly on fuel consumption, the ACEEE is more encompassing with its green standards. It includes comprehensive sustainability measurements for each car, such as the emissions of the estimated battery manufacturer if the car includes a lithium-ion battery.

"Vehicles running on electricity emit nothing from the tailpipe, but their 'upstream' emissions can be substantial, depending on where they're charged. As U.S. power generation becomes cleaner, these vehicles' scores will rise," ACEEE Transportation Director Therese Langer said in a statement.

The ACEE's full list of the 12 greenest vehicles for 2011 is as follows:

Honda Civic GX '

Nissan Leaf

Smart Fortwo cabriolet and coupe

Toyota Prius

Honda Civic Hybrid

Honda Insight

Ford Fiesta SFE

Chevrolet Cruze Eco

Hyundai Elantra

Mini Cooper

Toyota Yaris

Chevrolet Volt

The ACEEE also offers more consumer-friendly lists that rank cars within in each class and are divided by manual and automatic transmission. When it comes to large SUVs, for example, the Cadillac Escalade Hybrid wins first place.