"You know, there isn't a stinker here," muses St. Antoine while exhaling a gray-blue cloud of cigar smoke.

Our esteemed editor at large is correct in more ways than one. Despite our proximity to the tailpipes of three idling diesels, the dissipating haze of his Partagas Spanish Rosado is replaced by nothing but the cold clean scent of an eastern Sierra winter.

Equally striking is the conspicuous lack of traditional diesel clatter. That's to be expected of the fourth member of our quartet, the brand-new, eerily quiet 2010 Lexus RX 450h. It is a hybrid after all, but what about the BMW X5 xDrive 35d, Mercedes-Benz ML320 BlueTEC, and Volkswagen Touareg TDI? What does their burbling idle say about the state of modern diesels? Do they stand a chance against the latest hybrid version of the world's best-selling luxury SUV? We assemble in the mountains to find out.

Our pre-expedition walkaround reveals a few highlights. With an available third-row/seven-passenger configuration, the X5 is the most capacious of all. Though similar in overall length to the Benz and VW, the 107.9-inch wheelbase of the Lexus is shortest by 4.5 inches, a function of its car-based chassis.

Though zee Germans are all powered by 3.0-liter, six-cylinder turbodiesel engines, they differ in the details. BMW sticks by its impressive sequentially twin turbocharged inline-six architecture, while Benz and VW opt for single turbos and vee cylinder arrangements. All three require the latest ultra-low-sulphur diesel fuel and use proprietary variations of AdBlue urea injection to reduce nitrogen-oxide emissions. They run clean, but still can't touch the Lexus's SULEV status.

While the Benz retains its comparatively traditional 4-Matic full-time four-wheel-drive system, the X5 serves up Dynamic Traction Control, the rear torque-splitting trickery that puts the "x" in BMW's xDrive. The Touareg's 4XMOTION system is the only one to offer full-time four-wheel drive with low range, while the RX 450h again shows its hybrid-car roots. A transversely mounted engine and electric motor/generator power the front wheels, while an additional motor/generator spins the rear wheels on demand.