John Jechura, professor of practice in chemical engineering at Colorado School of Mines, was recently interviewed by Reuters about shale crude refining and its impact on jet fuel prices.
From the article:
Shale crude is younger than some other types of crude, so it differs somewhat from oil from other formations. The oil is a bit "waxier," like wax applied to skis, said John Jechura, a professor of practice in chemical engineering at Colorado School of Mines.
Refiners have found that when making diesel, their second-most common product after gasoline, they need to take measures to offset that waxiness to make the fuel usable for truck and car engines.