Check out the "Why are diesels better?" link in my signature. I wrote an argumentative essay on diesel versus gas a few years ago, for a class. Got a perfect score on it, too. The link is the text of the paper. AFAIK, all of the data's still valid.

Hope it helps some...good luck!

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2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999