With the price of diesel fuel undercutting gasoline, diesel-powered cars might be ready for a comeback in the United States. This is due to more stringent emission regulations and the recent availability of ultra-low sulfur diesel fuel (ULSD) that's compatible with the latest diesel engine technology. This results in cleaner emissions that allow these vehicles to be sold in all 50 states.

The Mercedes-Benz E320 (available to online subscribers) luxury sedan is part of the new wave of diesel cars to hit the market. We recently purchased an E320, and thus far, we have been quite impressed overall. Our E320's 3.0-liter V6 is remarkable. The engine is surprisingly quiet and pulls like crazy at almost any speed. While 208 hp might not seem like much, it's more than enough to move the E down the road with confidence. But at $55,415, it certainly isn't cheap. Do we think it's worth it? Here's a look at some comments our testers have written in the E320's logbook:

"Nice combo of sport and luxury."

"Excellent steering and agile handling."

"Mercedes just gets the ride control right."

"Effortless midrange thrust like that of a V8."

"Most people would never guess this is a diesel - excellent engine noise suppression."

"Could squeeze about 650-700 miles out of this tank of fuel."

"I love having the trip computer's 'range' function on and watch the numbers go UP...how cool is that?!"

"Very good visibility."

"Why can't I both display trip computer and use radio wheel controls - have to pick one or the other?"

"Controls are still the same old mistakes: too easy to hit cruise stalk [instead of turn signal]; climate display very small and faint; seat heaters that lower automatically and then shut down..."

"Cannot adjust the seat until the car is on or door is open - stupid."

"Limited rear seat room."

"$55K is a ton of money, but if I were doing lots of highway driving, this car would be my first choice."

"Comfortable and a joy to drive...one of the most amazing powertrains ever."

We're clearly impressed with this car's excellent combination of economy, comfort, and drivability. It is truly a rare breed. Stay tuned to see how it stacks up against the completion from BMW, Lexus, and Volvo.

--Mike Quincy