It was once generally assumed that performance and fuel efficiency mixed about as well as oil and water. Now, the green revolution has changed all that. Introduced last year, the Lexus GS 450h midsize luxury sport sedan offers a unique variation of the Lexus Hybrid Drive system. The 450h's 3.5-liter V6 engine and compact electric motor have been tuned with a performance bias. Combined, they produce a total of 340 horsepower, yet still deliver up to 30 percent better fuel efficiency than a similarly potent V8 engine, while allowing this Lexus to achieve Super-Low-Emissions Vehicle (SULEV) status.

Aside from its hybrid-specific instrumentation, wheels and badging, the 2008 Lexus GS 450h looks and feels much like its lesser GS 350 and GS 460 stablemates. This means it boasts the same rakish styling, exemplary fit and finish, refined ride and handling, and full complement of luxury and convenience features. In fact, being the flagship of the line, the GS 450h features the highest creature comfort quotient, with standard amenities that are optional on other GS models -- including a power rear sunshade, heated and ventilated front seats, rear side-impact airbags, rain-sensing wipers, adaptive front lighting, a rear back-up camera and a parking assist system.

Overall, the GS 450h's combination of performance and luxury is quite impressive. But we suspect the appeal lies mostly in its niche status. Beyond some of the inherent limitations of hybrid packaging -- like a small trunk -- the 2008 Lexus GS 450h is much less involving to drive than traditional luxury sport sedans like the BMW 5 Series. At the same time, truly green-minded consumers will likely find that this model doesn't bring about nearly the amount of fuel savings one might expect of a car with a hybrid badge. But those wanting maximum thrust with minimum thirst in a truly elegant wrapper will no doubt be entirely satisfied.

The 2008 Lexus GS 450h midsize luxury sedan sits atop the GS lineup. It comes equipped with a full array of standard premium luxury features such as 18-inch wheels, adaptive suspension dampers, adaptive xenon headlights and a sunroof. Leather upholstery, heated and cooled front seats, dual-zone automatic climate control, interior wood trim, Bluetooth, a back-up camera, keyless ignition and a 10-speaker audio system with in-dash CD changer and auxiliary audio jack also come standard.

There are a handful of additional options to choose from, including a navigation system, satellite radio, a phenomenal 14-speaker Mark Levinson audio system, a safety-oriented pre-collision feature with adaptive cruise control, active antiroll bars and a rear spoiler. Conventional summer (performance) tires are standard on the GS 450h, but buyers have the option of getting either summer or all-season run-flat tires.

The GS 450h's 3.5-liter V6 engine and separate high-output electric motor combine to generate up to 340 hp. The hybrid's power is transferred seamlessly to the rear wheels through a specialized continuously variable transmission (CVT). As with most hybrids, the GS 450h can start off under electric power and then engage the V6 automatically when additional motivation is needed. Maximum torque is available immediately, and performance is impressive at any speed, whether accelerating from a standing start or calling on midrange passing reserves at higher speeds. Zero-to-60-mph runs take a scant 5.2 seconds, and the gas/electric hybrid powertrain helps the 450h achieve an EPA-estimated fuel economy rating of 22 mpg city and 25 mpg highway. For comparison, the V8-powered GS 460 has a 17/24 mpg rating, and the BMW 550i has a 15/23 mpg rating.

Standard GS 450h safety equipment includes antilock brakes with brake assist, traction control and stability control. Inside are a total of 10 airbags, including front and rear seat-mounted side airbags, driver and front passenger knee airbags and full-length head curtain airbags. Optional items include Lexus Link communications and Lexus' Pre-Collision System. This latter bit of technology uses a radar sensor to detect objects in front of the car, plus a computer that tracks vehicle speed, yaw rate and steering angle. If the computer determines that a collision is imminent, it immediately activates the seatbelt pre-tensioners and engages brake assist when the brake pedal is depressed. For the GS line as a whole, the Insurance Institute for Highway Safety has issued a top "Good" rating for both frontal-offset and side-impact safety.

The 2008 Lexus GS 450h provides exceptionally composed and well-balanced performance, with a nearly perfect compromise between sport sedan responsiveness and touring sedan comfort. The ride is plush in the adaptive suspension's Comfort mode; when the driver is up for a more spirited romp, the Sport setting noticeably firms up the damping. When the optional active stabilizer system is added, body roll during cornering is also considerably reduced. Grip at the limit is superb in the GS 450h, thanks to the standard 18-inch Z-rated performance tires. One minor weakness involves the brakes, which some drivers find non-progressive and a bit touchy at first. This unusual pedal feel is quickly taken in stride, however, and the regenerative braking system otherwise stops the 2-ton GS 450h quickly and with reassuring authority.

In keeping with Lexus tradition, the GS 450h sports a luxurious and well-crafted cabin. Though spacious enough for five passengers, it accommodates four more comfortably as the elevated rear center cushion makes for a tighter fit in the middle position. Genuine wood and aluminum trim complements the rich leather seating surfaces, and it's all put together with flawless fit and finish. However, the highly polished wood can reflect glare annoyingly at times, and the control-oriented drop-down dash panel to the left of the steering wheel can get in the way of the driver's exit if left open. Trunk space is much tighter than other GS models at only 7.5 cubic feet, owing to the placement of the hybrid battery pack.