While its true that diesels are *slightly* dirtier than a gasoline car (more NOx, but virtually no carbon monoxide/evaporative emissions), the diesel engine's higher fuel efficiency reduces pollution along the entire fuel chain. Less fuel. Less tanker trucks. Fewer oil ships. Fewer wells.

That's why the EPA's GREET analysis *from well-to-wheel* ranks diesel-hybrids as cleaner than gasoline-hybrids & fuel-celled cars.