2012 Mercedes-Benz ML350 BlueTEC

The 3.0-liter turbodiesel V6 engine in the brand-new ML350 SUV is versatile. It's featured in the larger, three-row GL, the R-Class Minivan, the midsize E-Class and the flagship S-Class. You won't find a quieter or more powerful diesel engine in the segment, and it packs a walloping 455 lb-ft of torque. From within the BlueTec's plush, understated cabin, your only clues that this all-wheel-drive Benz has a diesel are the tachometer maxing out under 5,000 rpm and when you floor the gas. There's no need for the pricier V8 in the ML550 or the overkill ML63 AMG. The only downside is the AdBlue tank under the cargo floor, which contains a urea-based fluid that cleans the exhaust gas. It must be refilled at a Mercedes dealer or the engine won't start.

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2012 Volvo V60 Plug-in Hybrid

Picture a handsomer Chevy Volt with all-wheel drive and a high-quality interior and you have the basis for the Volvo V60 plug-in hybrid, a diesel-electric station wagon that can deliver more than 100 mpg. It uses a 2.4-liter 5-cylinder engine powering the front wheels and a 70-horsepower electric motor powering the rear. Volvo allows the driver to select three modes: electric, up to 35 miles; hybrid; and power, which puts down all 280 combined horsepower. Volvo even has a "save for later" function that recharges the battery so the driver can run on electricity for up to 12 miles without plugging back in. It will go on sale in Europe later this year. A U.S. version is still being considered.

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Mercedes-Benz E300 BlueTEC Hybrid

While the big S400 Hybrid featured little more than a mediocre start-stop system, this latest Mercedes hybrid takes efficiency more seriously. Like the Volvo, the E300 BlueTec Hybrid pairs the best of both torques — low-rpm diesel and a zippy electric motor — in a luxurious package. Unlike the Volvo's innovate plug-in layout, Mercedes uses a conventional rear-wheel-drive setup, pairing a 0.8-kilowatt lithium-ion battery — smaller than that in the Toyota Prius — with the company's tried-and-true 3.0-liter turbodiesel engine. The company claims up to 56 mpg and electric coasting speeds at up to 100 mph. A gasoline version could eventually make it to our shores, but place all bets against seeing this diesel.

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BMW M550d xDrive

Imagine cutting to 60 mph in less than 4.7 seconds and then cruising at 37 mpg, all while shuttling three other people in total comfort. Well, don't, because this BMW sedan is never coming to America. The M550d xDrive is the automaker's first diesel to appear with an M badge, the letter signifying BMW's motorsports tuning division. Not surprisingly, the M550d is a diesel rocket ship. The 3.0-liter inline-6 engine packs not two, but three turbochargers for an unheard-of 381 horsepower and 546 lb-ft of torque. Apparently, it is now possible to be excessive and frugal at the same time.

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Smart fortwo CDi

Smart doesn't have a bright future in America, and not just because the fortwo is barely larger than a coffee table. The fuel economy, at 34 mpg city/38 mpg highway, is disappointing for a car this small, and most buyers have chosen roomier compacts that get similar mileage with four doors and a real trunk. But if we had the fortwo's European diesel, Smart could finally make economic sense. That model features a 0.8-liter turbodiesel 3-cylinder engine with 96 lb-ft of torque, 28 more than our measly gasoline model. Plus, the diesel is rated at nearly 71 mpg, and in Environmental Protection Agency tests, it would likely top 60 mpg. Problem solved.

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Honda Civic i-DTEC

The rather boring, conservative styling on U.S. Civics, which Honda is already altering after heavy criticism, is nothing like the wild, space-age hatchback that Europeans enjoy. If sold here, it would handily beat the Civic Hybrid by many miles on the highway. The European Civic's 2.2-liter 4-cylinder diesel engine is rated at 67 mpg on European test cycles and packs a healthy 258 lb-ft of torque that leaves the U.S. Si performance trim in shame. Honda hasn't certified this engine for the U.S., but with the upcoming Chevrolet Cruze diesel, we imagine it's having second thoughts.

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Clifford Atiyeh is the automotive editor for The Boston Globe and Boston.com. He has contributed to The Times of London, The Wall Street Journal, Popular Mechanics, and spent his entire life driving cars he doesn't own.

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