They've been billed as the cars of tomorrow, and the early ones looked like futuristic vehicles right out of The Jetsons.

The part-fuel, part-electric autos known as hybrids are still just eking out a small niche among today's car buyers, but that isn't stopping hopeful industry giants from dreaming up new versions to sell — bigger hybrids, faster hybrids, better-equipped hybrids, even SUV hybrids.

Ford (F), General Motors (GM) and DaimlerChrysler AG (DCX)'s Chrysler unit have announced plans to unveil hybrid trucks — though Ford recently again delayed the release of its gasoline-electric Escape, this time until late summer of 2004. Ford announced plans to begin production on the vehicle in July and said it hopes to sell between 10,000 and 20,000 a year.

Honda is still offering its hybrid version of the Civic. And Toyota, a leader in hybrid vehicles to date, has a second-generation Prius that went on sale last month, as well as two SUV models — a Lexus RX 330 (search) and a Toyota Highlander (search) — on tap for 2004.

"We see the hybrid as a bridge to whatever the car of the future is going to be," said Wade Hoyt, a spokesman for Toyota Motor Sales USA Inc. He said Toyota plans to continue rolling out new hybrid vehicles for the foreseeable future.

Hybrids are vehicles with traditional gas-powered engines that also have electric motors and battery packs to improve fuel efficiency. They tend to cost between $1,500 and $4,000 more than their non-hybrid counterparts and need more frequent battery replacements.

But though hybrids still have kinks that need ironing out and currently seem to appeal mainly to the environmentalist set, some industry insiders say it's a lot more likely they'll shape tomorrow's transportation than the other model under consideration — the hydrogen-powered car.

"(Hybrids) are here and now," said Aaron Robinson, technical editor at Car and Driver magazine. "They're good because they allow you to put gasoline in the car. Hydrogen raises all kinds of issues as a fuel."

Chief among those issues is where to get the necessary amount of hydrogen. Even though the element is found in water, the amount of energy required to separate it from the oxygen is staggering.

"It requires about as much energy as you'll get out of it when you burn it," Robinson said. "The question is, where do you get that energy from? And if you're going to use solar, you'd need vast areas of solar the size of states to run cities full of cars. It's just unfeasible."

Chris Struve, a credit analyst from Fitch Ratings who specializes in the automotive sector, said he has seen estimates putting the costs of hydrogen production alone at between $50 and $250 billion. He doesn’t think converting hydrogen is the main hurdle; he sees the larger issue being the major changes the infrastructure would need to deliver hydrogen fuel.

Struve said at the earliest, hydrogen fuel cell cars will be available on the general market in 20 years.

"The problem is, you're going to start to hit the wall — you need support from governments" to continue the advances in fuel cell technology that have already been made, he said.

The other problem with hydrogen-powered cars is how to store and transport the hydrogen. Unlike most other gases, it gets hotter instead of colder when it expands, which makes hydrogen more dangerous than traditional fossil fuels.

"You can't have a situation where if you get rear-ended, you take out a whole city block," Robinson said. "That's just not practical."

But the federal government is still betting on hydrogen fuel cells in cars as a way to cut back on our country's reliance on petroleum. The Department of Energy (search) has set up the FreedomCAR & Vehicle Technologies Program (search) to develop fuel cells and other gasoline-free ways of powering cars.

"Fuel cells are 2-3 times more efficient than today's internal combustion engines," the FreedomCAR Web site states. "The Department of Energy has determined that developing hydrogen-powered fuel cell vehicles and the hydrogen supply infrastructure needed to support them offers a promising approach to reducing our nation's consumption of petroleum."

Though Toyota is currently testing a limited number of hydrogen cars, both Hoyt and Robinson are skeptical the vehicles will ever dominate America's roadways.

"The hydrogen car is kind of like the steam-powered car, which was a 19th-century solution to a 20th-century problem," Robinson said. "Hydrogen is a 20th-century solution to a 21st-century problem. I feel hydrogen will never truly replace gasoline."

As for hybrids, he isn't sure they're going to ever become all the rage, either.

"Hybrids are for people who want to make a statement," he said. "It's a rolling advertisement for a world view. There is a vein of people who want to show off their greenness, but most just want a car that holds all their crap and feels zippy. Hybrids aren't zippy."