When it comes to hybrid, the promise of greatly improved fuel economy is typically the biggest draw. But size and weight are the enemies of high fuel economy, as shown by the few "green" SUVs that are available. In a similar fashion, the 2011 Lexus LS 600h L falls victim to its 5,300-pound curb weight. To make matters worse, this hybrid luxury sedan will set you back a serious chunk of change compared to its conventionally powered stablemate.

Lexus claims that the 2011 LS 600h L will perform at the level of a V12-powered premium luxury sedan while delivering the fuel economy of a V8. In reality, the Lexus trails behind the 12-cylinder competition by a significant margin and offers little fuel economy benefit compared to the regular gas-only LS. The LS 600h L has an EPA-estimated combined average of 20 mpg, just 1 mpg ahead of the LS 460 L's 19 mpg combined figure. The hybrid also sets your bank account back quite a bit more, with an MSRP approximately $40,000 higher than a comparably equipped LS 460 L.

There are, however, a few bright spots in the 2011 Lexus LS 600h L's otherwise dim outlook. As a super-ultralow-emissions vehicle (SULEV), this hybrid justifies at least some of its green leanings. As a Lexus flagship, it also delivers exceptional luxury in the form of a finely crafted interior that is as quiet as a crypt. You also get a few more standard features with the 600h L.

But the few positives do little to dissuade us from recommending a long list of other luxury sedans over the 2011 LS 600h L -- including its own LS 460 L cousin. For the eco-conscious buyer, the 2011 BMW 7-Series with its line of Active Hybrid sedans are priced well below this Lexus, as is the 2011 Mercedes-Benz S400 hybrid. For the performance-minded shopper, models like the 2011 BMW Alpina B7, 2011 Jaguar XJ and 2011 Porsche Panamera are all considerably better choices.

The 2011 Lexus LS 600h L is a full-size hybrid luxury sedan based on the long-wheelbase version of its gas-powered LS 460 sibling. As the most expensive model in the Lexus lineup, this flagship is as fully loaded as anything you'll find.

Included in the six-figure price tag are 19-inch alloy wheels, LED projector headlights, keyless ignition and entry, power door closers, the Lexus Advanced Parking Guidance System (which automatically steers the car into a parallel parking spot), parking assist with a back-up camera, a hard-drive-based navigation system (with real-time traffic and weather, USB/iPod connectivity and Bluetooth streaming audio), leather-trimmed seats and interior and a heated steering wheel.

Other standard features include a Cold Weather package (windshield de-icer and high-output heater), a 16-way power driver seat and 12-way power passenger seat (with memory for both), heated and ventilated front seats, heated rear seats, a power rear sunshade, Lexus Enform telematics, Bluetooth and an earth-shaking 19-speaker Mark Levinson surround-sound system (with six-disc CD/DVD changer, satellite radio, a music server with a 2,000-song capacity and auxiliary/USB input jacks).

As if all that were not enough, Lexus offers a couple of option packages to further pamper occupants. Package content and availability does vary from region to region. The Premium Package II includes four-zone climate control, a center console with a cooler box, power rear door shades, additional wood trim, a rear audio control panel, rear heated and cooled seats, a rear-seat entertainment system and rear-seat side airbags.

The Executive-Class Seating Package II adds a power recliner with leg rest and massage feature for the right rear seat, a fixed rear center console that eliminates the fifth seating position, a rear-seat wood table, infrared temperature sensors that adjust the climate control for the rear passengers and special 18-inch, nine-spoke wheels. In most cases, the only stand-alone option is adaptive cruise control with a pre-collision safety system.

The 2011 Lexus LS 600h L is powered by a full hybrid system made up of two electric motor/generators and a 389-horsepower 5.0-liter V8. With all motors working together, peak output is 438 hp. Power is routed to all four wheels through a specialized continuously variable transmission (CVT) that features manual shift control. The transmission also has three driver-selectable driving modes -- Normal, Power and Snow -- for changing road conditions.

Like other Toyota-built hybrid systems, the LS 600h L's can propel the car solely under electric power at low speed and for limited distances. The air-conditioning system runs off electric power, allowing the gas engine to shut down at stops. And like other related hybrid systems, this system recharges the battery pack via regenerative braking when decelerating.

In recent testing, we only managed a 0-60-mph time of 6.0 seconds -- a tenth of a second slower than a gas-powered LS 460 L we tested. Equally disappointing is the fuel economy, registering an EPA-estimated 19 mpg city/23 mpg highway and 20 mpg in combined driving, which isn't much different from the regular LS 460 L's 16/24/19 mpg. The one bright spot concerns the hybrid's lower emissions -- as mentioned before, it earns SULEV status. Still, the conventionally powered LS boasts a clean ULEV rating.

Standard safety features on the 2011 Lexus LS 600h L include traction and stability control, front-seat side airbags, full-length side curtain airbags, knee airbags for the front seats and Safety Connect emergency telematics. Rear-seat side airbags are included with either option package. If the LS is equipped with the optional adaptive cruise control, a pre-collision system senses impending frontal impacts and automatically pre-tensions seatbelts and boosts braking power.

In recent Edmunds brake testing, an LS 600h L came to a stop from 60 mph in 120 feet -- about average for this class. In crash testing conducted by the Insurance Institute for Highway Safety, the Lexus LS scored the highest rating of "Good" for its protection in frontal-offset impacts.

It would be a difficult challenge to find a luxury sedan as quiet as the 2011 Lexus LS 600h L. With initial power supplied from the electric motors alone, acceleration from a stop is eerily silent. The supple suspension easily absorbs any road imperfections, while the sound insulation isolates all occupants from the world outside.

If the Lexus LS has been criticized for anything, it's a lack of passion in its driving experience, the same thing that can be said for the LS 600h L. The machinations of the hybrid system, while subdued, add another layer of insulation between the driver and the road. As an automotive isolation chamber, the LS 600h is among the world's best, but this is not a sport sedan by any stretch of the imagination.

In terms of sheer luxury, you'd probably have to acquire an executive jet to rival the Lexus 600h L's cabin. Most surfaces are covered in supple leather accented by rich wood trim. Adding either of the optional packages will elevate the interior to Rolls-Royce or Maybach territory for comfort and space. As with other Lexus instrument panels, the LS 600's gauges are strikingly sharp and legible. Unfortunately, much of the LS 600h L's trunk space is taken up by the hybrid and rear climate control components, dropping maximum luggage capacity to only 10 cubic feet, which is less than most compact car trunks.