"To meet the same emissions standards with a diesel, you're looking at almost two times the variable cost for an OEM. And the after-treatment is another thousand, 2,000, maybe even 3,000. You're either adding $6,000 to the price or you're just doing marketing."

Obviously, Hyundai sells a number of such vehicles in Europe, where the market for diesels is far larger. But in the U.S., the cost can be prohibitive for an automaker that, like Hyundai, has worked hard to position itself as the value leader below its commuter and near-luxury (or, in the case of the Genesis, actual luxury) segment competitors.

Krafcik also pointed out that regular gasoline engines, thanks to direct injection and more efficient turbocharging methods, are moving up the ladder to compete with diesel engines' fuel efficiency.