This study by CNW found that, contrary to what seems intuitive, hybrid cars actually produce more pollution than many SUVs during their life cycle. This study, while hotly debated, certainly proves the "law of unintended consequences".

just as drivers are beginning to become comfortable with the technology, the long lineup of experimental and prototype hybrid systems being developed four years ago are ready, or nearly ready, for prime time—including three that use no electricity.

Hybrid SUVs use less fuel than conventional SUVs, but still use more fuel than small or midsize cars. Furthermore, hybrid SUVs tend to be heavier than regular SUVs, eroding fuel efficiency.