Measuring the energy efficiency of a new vehicle is one thing, but ascertaining its overall environmental impact can be more complex.
A debate still rages over the overall carbon footprint of electric cars compared to those powered by fossil fuels.
But for the past 20 years, the the American Council for an Energy-Efficient Economy has tried to come up with some concrete answers.
DON'T MISS: Hyundai Ioniq Electric beats Prius Prime, BMW i3 on energy efficiency (Nov 2016)
Every year, the ACEEE issues rankings of the environmental impact of new vehicles sold in the U.S.
Today, it issued its 2017 Greenest List, naming the 12 vehicles with the highest scores on its scale of environmental friendliness.
This year, the 2017 Hyundai Ioniq Electric topped the list, followed closely by the 22-kilowatt-hour version of the BMW i3.
2017 BMW i3
Both models received a score of 64, but the i3 scored slightly lower than the Ioniq on the environmental-damage index that factors into the final scores.
The third-place Toyota Prius Eco and fourth-place Fiat 500e received scores of 62, while the Nissan Leaf followed in fifth place with a score of 60.
Just behind the Leaf in sixth place was the Chevrolet Bolt EV, which shared its score of 59 with the seventh- and eighth-place finishers.
ALSO SEE: ACEEE Names 'Greenest' And 'Meanest' 2016 Cars (Jan 2016)
They were the Kia Soul EV and Toyota Prius Prime, respectively.
As was the case last year, every car on the Greenest List featured some form of electrification.
Of the 12 cars on the ACEEE Greenest List, seven were battery-electric, one was a plug-in hybrid (the Prius Prime), and four were conventional hybrids.
2017 Mercedes-AMG G65
The Greenest List is paired with what ACEEE calls the Meanest List, those 2017 vehicles that are the least environmentally friendly of any on the market.
That list of 12 vehicles included seven large SUVs: the Lexus LX 570, Toyota Sequoia, and five Mercedes-Benz models.
The Mercedes contingent included no less than three versions of the German automaker's G-Class off-roader, with the AMG G65 model topping the list as the "meanest" 2017 vehicle of all.
The ACEEE also named one version each of the Chevrolet Express and Ford Transit commercial vans, and the Toyota Tundra pickup truck.
The only two passenger cars on the list were once again the Bentley Mulsanne and Continental GT/Flying Spur, a pair of massive luxury models offered with turbocharged W-12 engines.
2017 Toyota Prius
In a nod to buyers for whom many plug-in electric cars are not locally available, the ACEEE also issues a Greener Choices list of the most environmentally-friendly gasoline vehicles.
This year, hybrids locked down the top four spots, with the Toyota Prius Eco taking top honors, followed by the same maker's smaller Prius C, then the Kia Niro FE, and Prius V.
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Vehicle scores on all three of the ACEEE's lists are largely based on full life-cycle emissions of both greenhouse gas and criteria pollutants (CO, HC, and NOx).
That includes estimates of emissions from fuel sourcing, transportation, and distribution, as well as emissions related to electricity generation.