A careful cost/benefit analysis of the diesel-powered 2009 BMW 335d sedan vs. the gasoline-powered BMW 335i is certain to yield...exactly nothing. There are many reasons for this:

1. The 335d burns less fuel than the 335i, no question. Yet diesel fuel also costs more than gasoline.
2. The 335d costs more than the 335i. Yet it also emits less CO2.
3. The 335d can easily exceed 500 miles on one tank of fuel. Yet the 335i is quicker, lighter and handles better.

Shall we continue? As with most alternative-fuel vehicles, the decision to buy the diesel-powered 2009 BMW 335d will be made by the heart more often than the pocketbook. Even so, the resolutions to the dilemmas above aren't easy to find, but here's how we see it:

1. Fuel cost is a wash. In this case, less fuel consumption cancels the price premium of diesel fuel. Most buyers shopping for a $50,000 sedan won't be splitting these hairs anyway.
2. The 335d costs $2,475 more than an identically equipped 335i, yet uses less fuel and emits fewer greenhouse gases. This seems like a small premium for anyone who prioritizes the planet and can afford a car this costly.
3. Who doesn't want to fill up less frequently? We'd bet it's the same folks who care more about CO2 emissions than they do about 0-60-mph times.

Numbers Big and Small
The 2009 BMW 335d is one of two vehicles introducing BMW's clean diesel technology to the U.S. this year (the other is the BMW X5 xDrive35d) and it generates some staggering numbers. Most striking is the output from its twin-turbo 3.0-liter inline-6: 265 horsepower at 4,200 rpm and 425 pound-feet of torque at 1,750 rpm.

All this snort goes to the ground through just one transmission option, a six-speed automatic with a manual shift mode. This is the same gearbox offered in the 335i, and it has the same sport mode that hangs onto gears longer. Our test car was fitted with the optional shift paddles on the steering wheel.

Look critically at the engine's output numbers and you'll see a relatively high power peak for a diesel engine that still retains plenty of low-end, rubber-torturing torque. This is a rare combination. This 3.0-liter inline-6 is capable of burying you in the seat with grunt, yet it still enjoys the drivability at high rpm (the redline is 5,000 rpm) needed for sporting character. It's a unique and entertaining combination.

This kind of flexibility comes courtesy of the two turbochargers — a small one optimized for quick throttle response and a larger one that takes over quickly to produce the bellowing torque. BMW utilizes urea (which it calls AdBlue) injection in the exhaust to reduce nitrous-oxide emissions.

This technology working in conjunction with a diesel particulate filter means the 335d's emissions are clean enough that it can be sold in all 50 states. The 6.1-gallon urea tank is simply refilled at the same intervals as a standard change of engine oil, so no special service is required. Urea refills are included in BMW's service program for four years or 50,000 miles. It's also impressive that BMW managed to jam this much storage volume into the 3 Series with no significant packaging compromises.

Taking Its Measure
As long as we're talking about striking numbers, here's another one: $50,895. That's what this 2009 BMW 335d test car costs with its leather upholstery and trim, the Sport package, keyless ignition and several other options. Its base price including destination is $44,725. Since it's a clean diesel, it qualifies for a $900 federal tax credit, which relieves a tiny bit of the sting. It also narrows the gap to an identically equipped 335i from the aforementioned $2,475 to only $1,575.

Now we're talking, and here's why. Using the EPA's fuel-economy figures for both cars (27 mpg combined for the 335d and 20 mpg combined for the 335i) and a rate of 15,000 miles driven annually, we find that the 335d will burn 195 gallons of fuel fewer than a 335i. In our own testing, we achieved 29.6 mpg with the 335d while covering 1,517 miles, about 70 percent of which were highway miles. Using the current average U.S. fuel prices for diesel and gasoline, the annual fuel cost at this rate is virtually the same — $1,273/year for the 335d and $1,263/year for the 335i.

At this rate, it will take prohibitively long to make up the price premium you pay for the diesel-powered 3 Series in the savings in fuel cost. By virtue of burning less fuel, however, the 335i also emits considerably less CO2 every year — 7.79 tons/year vs. 9.76 tons/year. So the answer for those whose hearts are green is simple: Buy the 335d.

Still, there are other benefits to consider.

Goes Like Stink, but Doesn't
The 335d's acceleration is impressive. At the track it hits 60 mph in 5.9 seconds (5.6 seconds with 1 foot of rollout like on a drag strip). It busts through the quarter-mile traps in 14.1 seconds at 99.1 mph. This is 0.6 second slower to 60 mph than the 335i, a gap that is maintained to the quarter-mile mark, and the trap speed is about 4 mph down on the gasoline-powered car.

The story the numbers don't tell is how effortlessly the diesel gets the job done. This power plant is amply engaging below 3,000 rpm. We found ourselves outrunning everyone while grunting it around town without ever approaching the upper reaches of the tachometer.

Venture beyond 3,000 rpm and you'll find enough life left in the top third of the tachometer to make hard driving enjoyable. And you'll do it without feeling like you're overworking the engine. When we start driving quickly, we inevitably end up spending lots of time around redline, and we've found this diesel will play in that arena with a willingness to rev all the way to redline.

Even though the 2009 BMW 335d features an aluminum-block engine, there's still a weight penalty associated with the diesel sedan compared to the 335i. Nevertheless, the 335d offers the typical feel and response through the controls of a BMW 3 Series. Intuitive and well weighted, the 335d's steering feels rewarding, despite the fact that this car weighs 3,804 pounds, 191 pounds more than the 335i. Turn-in is good and the overall sense of control doesn't suffer from the added weight.

With a 67.3-mph performance through the slalom, the 335d is a few ticks slower than the 335i, yet it punches through the cones with similar confidence. It retains a weight distribution of 51 percent front/49 percent rear despite a heavier engine and accompanying components. On the skid pad, the diesel proved as good or better than any 335i we've tested, with a performance of 0.91g thanks to 225/40R18 front and 255/35R18 rear Bridgestone Potenza RE050A run-flat tires.

According to BMW, this car's Sport package gives it the ability to reach 149 mph, just 1 mph short of the 335i's terminal velocity. Go ahead, tell us there isn't some novelty in a 150-mph diesel that pulls 0.91g on the skid pad.

Diesel? Really?
Even if there isn't novelty and you just happen to like the perfume of diesel fuel in the morning, then you've got a perfectly good 3 Series sedan that makes almost no compromises as a diesel.

Like most modern non-commercial diesel engines, this one is virtually silent. You'd never know this twin-turbo inline-6 is a diesel. When you get into the throttle of most diesel engines, it's as if someone turned up the volume control to 11. But when you rev this BMW diesel, your sound perception gauge barely goes up to 2.

One potential drawback is the fact that you'll occasionally have to search for a fuel station that sells diesel. And, sometimes, when you do, it will be a truck stop complete with the greasy mess of diesel spilled at every pump and slathered on every handle. We only had to deal with this once in five fills.

Still a 3 Series
Inside the diesel's cabin are the familiar instruments, seats, steering wheel and sense of quality that you associate with a 3 Series. You really do get what you pay for here.

And there's no indication that this is a diesel either, just the same materials and design as the other cars in the line of 3 Series cars. Diesel-powered 3s are even available now with the same options as the 335i, except active steering — a feature we doubt many will miss.

So what we have here is a class-leading sedan with plenty of grunt, lots of range and a large price tag. Thing is, if you're shopping in this price range and have an ounce of social responsibility in your soul, then the 2009 BMW 335d is undeniably appealing. There isn't another car that can match its strengths. And it doesn't have many weaknesses.

You don't even need a cost/benefit analysis to tell you that.