I would be interested if anyone can comment authoritatively on the economics of diesel fuel: I have heard from one source that diesel fuel is distinct from gasoline, in that diesel is a petroleum middle distillate and comes out of a refinery separate from gasoline (and kerosene etc). So that if the US vehicle fleet as a whole were to switch from gasoline to diesel in order to take advantage of diesel's benefits, its not so much a matter of switching over production of gasoline to diesel to meet the higher demand (because you can only get x amount of diesel from y barrels of petroleum), its a matter of importing more petroleum to make more diesel, and possibly raising prices for an ever scarcer diesel fuel. In other words, the US is still in global competition with other consumers for that barrel of oil, whether that barrel yields diesel or gasoline or both.

Disclaimer: I own three gas-consuming cars and I swear I'm not at the sharp end of some anti-diesel community, I would like an answer to the question though: if the US were to see a 20, or 50% increase in diesel demand from autos, what happens to petroleum demand (from which gas and diesel are made), and what happens to diesel prices, to answer the demand?