I think Econbrowser deserves some credit, he is an economist who, while he doesn't agree with the premises of peak oil per se, he's a lot more open minded about peak oil than Levitt demonstrated in his screed we talked about yesterday.  JDH has a post of interest (though HO has talked a lot about the types of crude, the problems with refining it, and the like around here before) over at this place.

Not all the black gooey stuff that comes out of the ground is the same. Crude oil produced by different fields differs importantly in viscosity and sulfur content. The more viscous crudes (as measured by a lower API gravity) are called "heavier," and those with higher sulfur content are called "sour" (as opposed to low-sulfur "sweet" crude). The heavier and more sour the crude, the more difficult and expensive it is to turn into usable refined products. The price of oil you usually hear quoted (such as the recent highs of $67 a barrel) is the price of a light, sweet grade like West Texas Intermediate.

Of course, there's more to the story than this, but kudos to JDH for paying attention.  I am sure HO will have something to say about this soon.  :)

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