It’s a volatile time to be making and marketing petroleum-fueled automobiles.

Every company wants to be “green,” or at least seen as green. Every auto maker knows it’s the coming thing, and at this point, it’s perilous to be perceived as anything but totally engaged in environmental awareness.

The irony, however, is that extracting the green in the wallets of well-heeled customers remains seated on an inconvenient truth: power sells.

Certainly nobody wants to be the last company pushing gas guzzlers – but for auto makers in the premium segments, it’s now a bizarre game of chicken: We’ll start saving the planet when our competitors do.

You have to wonder about the long-term viability – or sheer audacity – of coming to market in ’08 with a message of, “Have another half-liter and another 80 hp, why don’t you?”

That’s the space Mercedes-Benz U.S.A. is occupying, though, with the revised ’08 ML 550 and GL 550 SUVs. We never heard many complaints about the rorty, 302-hp 5.0L DOHC V-8 that propelled last year’s ML 500, but the larger 5.5L unit nonetheless deals out an additional 80 ponies. Really, we didn’t know anybody was asking.

No, it’s more about keeping up with the Joneses – particularly if they’re shopping V-8- powered versions of the German competition, the BMW X5 (350 hp), Porsche Cayenne S (385 hp) and Audi Q7 (350 hp), not to mention Range Rover (305 hp) or perhaps even Cadillac Escalade (403 hp).

Maddeningly inconsistent or not, buyers and manufacturers agree: The polar ice caps may be melting, but Jimmy’s late for school and 300 horses isn’t going to get it done.

Part of this arms race is attributable to the bloat that’s taken hold of this class.

The revised X5 is the newest of the breed, the 4.8i smashing the scales at 5,335 lbs. (2,421 kg), and the Q7 is anything but dainty at 5,269 lbs. (2,390 kg). The Escalade? Guess 3 tons and you won’t be far from the mark.

So the ’08 ML 550 is a class featherweight at 4,819 lbs. (2,185 kg) – hustling behind its fresh 382-hp rating from 0-60 mph (97 km/h) in a giddy 5.6 seconds, a couple eyeblinks slower than some exotic cars.

For the GL 550, the new 5.5L V-8 yields just a 47-hp hike over the 4.6L V-8 that’s still available for the GL 450. Hitting the pavement with 461 lbs. (209 kg) more bulk than the ML 550, the case for the upgrade to the 5.5L V-8 is more understandable.

Regardless of the new 5.5L’s political-correctness factor, it is an irrefutably fine experience.

The throttle response – helped by a new 2-stage intake manifold – is always immediate and linear, and the 391 lb.-ft. (530 Nm) of torque peaks from 2,800-4,800 rpm, making acceleration through the sometimes-undecided but crisp 7-speed automatic a frothy romp at almost any road speed.

Mercedes will argue this performance comes at virtually no cost because the outgoing ML 500, for example, skated on the Environmental Protection Agency rollers to the tune of 14 mpg (16.8 L/100 km) in the city and 19 mpg (12.4 L/100 km) highway, while the new ML 550 turns in 13 mpg (18 L/100 km) and 18 mpg (13 L/100 km) – under the EPA’s markedly less-generous new economy ratings that began for ’08.

Ah, but that’s the same sort of “justifiable” creep we’ve seen for years with curb weights, too; auto makers say they have no choice. To borrow from the film “Cool Hand Luke,” “Callin’ it your job don’t make it right, boss.”

The GL 550 does 1 mpg (.04 L/100 km) worse than the ML on the highway.

With the new engine, the ML 550 is the recipient of extra bodywork from the AMG tuner unit, and the GL 550 has some specific details, too. Both vehicles’ well-executed interiors are untouched.

At $53,175, the ’08 ML 550 seems almost a bargain. Less so the GL 550 at a rollicking $77,750 – a model that seems better served in these green-leaning times by the fine 3.0L V-6 turbodiesel that churns out even more metal-moving torque than the scalding 5.5L V-8, provides nearly 40% better fuel economy and is $24,000 cheaper.