????With diesel fuel cheaper than premium gasoline in parts of the country, it seems like a good time to compare a trio of diesel-powered vehicles from Germany — one each from Volkswagen, Audi, and Mercedes-Benz

????The question I want to answer: Are diesels fated to remain bit players in America or are they ready for prime time?

????For the driver, the diesel experience is a bit different from the typical gasoline-powered car. The noise, odor, and slow startup on cold days are a thing of the past. But diesel drivers find themselves going further between fill-ups — 600 miles or more in some cases. Good thing, too, because they will often have to drive miles to find a gas station with a diesel pump. That pump, in turn, may be isolated from the others, poorly maintained, and decrepit enough to have been installed around the time of the Korean War.

????On the plus side, the new generation of clean diesel engines is sturdier than its gasoline counterparts, has fewer parts, and can be easier on the environment. Since they get up to 30% better mileage, they produce 30% less carbon dioxide — a greenhouse gas.

????For those curious about diesels, the 2010 VW Golf TDI is a good introduction. With a base price of $22,590, the diesel Golf is $3,400 more expensive than a gasoline one for a higher diesel premium than the two other cars in this test. Fuel economy is impressive at 30 mpg city/42 highway, though if you drive 15,000 miles a year, you will need nine years to save enough on fuel to pay the higher cost. On a couple of occasions, I thought I detected a hesitation while accelerating that cut into my passing speed. But it wasn’t enough to diminish the bragging rights that come with owning a sophisticated piece of German technology for a reasonable price.

????Next on my schedule was the Audi Q7 TDI Quattro. The Q7 weights more than two and a half tons and the diesel ads another 350 pounds. But the price premium is relatively modest: $2,200 more than for the standard V-6, which brought the base price to $50,900 (with options, my test car cost $59,025). That will look like a bargain compared to the Mercedes. Still, both in its humpback profile and its sluggish responses, the Q7 never stopped reminding me of its substantial mass. I would sacrifice the third row of seats and go for the more nimble Audi Q5.

????The last diesel I drove proved to be a pleasant surprise. Although it is heavier than the Q7 by a couple of hundred pounds, the Mercedes-Benz GL350 BlueTEC felt lighter, thanks to its well-balanced steering and responsive acceleration. Mercedes only has a gasoline-powered V-8 option for the GL at $61,450, so the V-6 diesel looks like a bargain at $59,950. This being a Mercedes, though, optional equipment pushed the as-tested price up to $73,385. Still, the Benz diesel was the smoothest of the three and delivered exceptional fuel economy. Although it was rated at 17 mpg city/23 mpg highway — less than the Audi — I occasionally found myself getting 27 mpg while cruising at 65 mph.

????After driving all three vehicles, I concluded that diesel is ready for prime time, but it doesn’t have enough natural advantages to make it more than a niche player. Absent some form of stimulus by the federal government in the form of tax credits for the purchase of a diesel car, or lower taxes on diesel fuel, it is likely to remain a minor power player.