The Top Ten: Most Polluting Cars, 2006

NOTE: MPG = miles per gallon. 1. The green score runs on a scale from 0 to 100. The top vehicle this year scored a 57, and the worst gas-guzzler scored 12. The score is based on automakers' test results for fuel economy and emissions as reported to the EPA, as well as an estimate of pollution from vehicle manufacturing, from the production and distribution of fuel, and from vehicle tailpipes. It also factors in air pollution.

Source: American Council for an Energy-Efficient Economy (ACEEE).