Patricia Monahan, Senior Vehicles Analyst for UCS writing in the HybridBlog says: Honda, Mercedes-Benz, DaimlerChrysler and VW are all planning on selling diesel cars, touting their 20 to 30 percent superior fuel economy over comparable gasoline models. ... A gallon of diesel fuel takes more oil to produce and it produces more greenhouse gases than a gallon of reformulated gasoline (with ethanol). This means you should cut the diesel fuel economy by as much as 15% when comparing it to a gasoline model. ... Diesel cars don't have sophisticated pollution monitors-—like gasoline vehicles do— to catch systems when they fail. So long-term use and emissions impact is still very much up in the air. In all, there are reasons to be both excited, and wary, about the new diesel cars we'll soon be seeing on the market.
I wonder what the comparison is on biodiesel. With very limited supplies of biodiesel, the use of biodiesel is likely to be limited to areas of the U.S. where there are biodiesel supplies. Until or unless FT diesel becomes available drivers in the U.S. are largely forced to use petroleum diesel.