Despite the dramatic drop in gas prices in recent weeks, hybrid vehicles remain a bright spot in an otherwise dismal American car market. There s just one problem: When it comes to reaching the promised land of optimal fuel efficiency, some hybrid owners are starting to ask a question: Are we there yet?

Green-minded drivers shopping for fuel sippers are finding that unless it s a gold-standard Toyota Prius or Honda Civic (each promising 45 highway mpg), the current crop of hybrids offer surprisingly measly mileage. Half of the 2009 hybrids rated by the Environmental Protection Agency, from the Cadillac Escalade to the Lexus LS 600h L, barely crack 25 mpg.

Automakers say part of the problem may actually be American driving habits, which are still far from green-friendly. They also point out that many customers are happy with at least some improvement over their SUV days understandable, considering that a nonhybrid two-wheel-drive Escalade, for one, gets only 15 mpg. Indeed, with most hybrids besting their conventional models mileage by at least 10 percent, environmentalists see the gains as something to build on. It s a start, says Jim Kliesch, a senior engineer with the Union of Concerned Scientists, a nonprofit environmental advocacy group.

But analysts say the hybrid story is a little more complicated and that manufacturers share as much blame as the aggressive, lead-footed American driver. Detroit automakers, in particular, came late to the hybrid party in terms of research and development. Not only did they launch their first model into the U.S. market nearly five years after the Japanese, but critics point out that the vehicles they initially chose to hybridize were not necessarily those that would yield the maximum green benefit. According to a J.D. Power survey, consumers think hybrids should deliver a 68 percent improvement over conventional models. That s totally unrealistic, says Mike Marshall, director of automotive technologies at J.D. Power.

Gas-and-electric cars may seem like a new-millennium invention, but engineers were actually tinkering with the technology as far back as 1900, when a young automotive upstart named Ferdinand Porsche added a combustion engine to his pioneering Elektromobil. The idea largely went fallow until the 1960s, when a handful of eco-friendly engine designs slowly began to emerge and then sputter. It wasn t until 1994, when a Toyota executive challenged his company s engineers to double their current cars fuel efficiency, that the technology finally took off. The product of that challenge, the Prius, hit the American market in 2000 and has led the green-car charge ever since, helping Toyota garner a whopping 79 percent of the hybrid market.

The Prius tantalizing mileage (45 highway, 48 city) makes the rest of the field look bad: Most current hybrids top out in the upper 20s to low 30s. The 2009 Chevrolet Malibu hybrid sedan earns a combined city/highway rating of 29 mpg, just three miles better than its conventional counterpart. The Lexus GS 450h, a larger luxury sedan, clocks in at 23. And the eight-cylinder, four-wheel-drive Chevy Tahoe SUV? Try 20.

The industry says that hybrid drivers need to be a lot better behind the wheel, since these vehicles require a whole new way of thinking and handling. Unlike conventional cars, hybrids get their best mileage in stop-and-start city driving, since the electric motor kicks in at low speeds and the engine shuts off instead of idling. They also get a boost from regenerative braking the transfer of energy from the brakes to the battery packs. Many drivers find themselves having to adopt a gentler driving style: no slamming on the brakes, no gunning the gas and embracing the fine art of coasting.

But drivers aren t the only ones struggling to get it right. Critics point out that many carmakers have adapted the technology to some of their least efficient and highest-priced vehicles: full-size SUVs and luxury cars. Instead of going with the six-cylinder Yukon SUV, GM gave the less economical eight-cylinder model a hybrid engine. At Lexus, the eco-minded driver can choose from only three models, including the RX 400h SUV hardly a fuel sipper at 25 mpg combined city and highway. Makers went for low-hanging fruit, says engineer Kliesch. GM s Executive Director of Hybrid Powertrains Larry Nitz acknowledges that large SUVs are his company s historical strength, but putting hybrid technology in them makes the most sense because those vehicles consume the most fuel. Problem is, they barely sell. GM s hybrid full-size SUVs (at nearly $50,000 a pop) move just a few hundred units a month, compared with more than 10,000 monthly Priuses. And that, Kliesch points out, doesn t save the country much gas.

Indeed, manufacturers still seem to be scratching their heads about what sells. Honda pulled the plug on its hybrid Accord in 2007 after years of weak sales. Pricey and not very fuel efficient it only got 27 mpg in city/highway driving the car sold in far fewer numbers than its chief rivals, the Toyota Prius and Camry. When the Accord came out, we were still in the learning stages, says Honda spokesperson Chris Naughton. Honda has since refocused on small, highly fuel-efficient hybrids, with three new models planned for the next few years. Its lesson from the Accord? When it comes to hybrids, says Naughton, customers main expectation is maximum fuel economy.

Even if gas prices continue to decline, the outlook for more-efficient hybrids seems promising. Manufacturers, including Ford, GM, Honda and Toyota, plan to goose mileage incrementally upward with design enhancements like better aerodynamics, tires with lower rolling resistance and engine upgrades that will allow for greater use of the electric motor. The third-generation 2010 Prius, for instance, is getting a full overhaul, complete with solar panels to run the air-conditioning.

And around the corner? The first plug-in hybrids, coming from GM and Toyota. Hardly the dinky electric cars of yore that could barely get you to work, they ll use lithium-ion batteries that can recharge from an external power source and should boost mileage into the 60s or higher. GM s Chevy Volt, slated for 2010, goes a step further: Designed to get 40 miles on a single charge before switching to gas, its projected mileage is fasten your seat belts 100 mpg.