The latest Los Angeles Auto Show illustrates the wide range of ways the auto industry is achieving higher gas mileage and lower emissions.

Green technologies range from futuristic fuel cells that combine hydrogen and oxygen to produce electricity, to more down-to-earth methods for conventional, internal-combustion engines to save gas.

Fuel-cell concept cars shown at the LA Auto Show -- held Nov. 21 to Nov. 30, 2008 -- include the Honda FC Sport. While promising, fuel-cell cars are still years away from being available to ordinary retail customers.

Scientists have been experimenting with fuel cells for decades, as far back as earlier generations of space flights. Technological advances have shrunk fuel cells to where a powerful "stack" of fuel cells will fit into a car, but they're still bulky and generate a lot of heat. Retail distribution and onboard storage of hydrogen fuel are also huge obstacles.

However, fuel cells have great appeal since the only tailpipe emission is pure water vapor. The notorious Los Angeles "smog" inspired the toughest emissions-control standards in the United States beginning in the late 1960s, so LA is an appropriate setting to show fuel cells.

In addition, the LA Auto Show is traditionally a showcase for Asian automakers -- most have their U.S. headquarters in Southern California.

However, the U.S. automakers were much in evidence in Los Angeles, too. For instance, the battery-powered Dodge EV Concept made its auto show debut in LA. Parent Chrysler said it could produce the Dodge EV as soon as next year. Chrysler's bankruptcy filing April 30 could serve to delay future products, but so far the company hasn't specified one way or the other with regard to specific product lines.

Hybrids, unlike fuel cells or electric vehicles, are widely available today. Hybrids combine an electric motor with a conventional, internal-combustion engine. At start-up and at low speeds, most hybrids run exclusively on battery power. The gasoline engine kicks in at higher speeds or when accelerating hard.

Engineers are concentrating on improvements like extending the zero-emissions, electric-only range of hybrids. The Ford Fusion Hybrid and its twin, the Mercury Milan Hybrid, are examples from the Los Angeles show. They can go much faster on battery power than earlier hybrid systems, according to Ford.

In practical terms, incremental improvements to conventional gasoline-powered cars may offer the quickest way to reduce air pollution from automobiles.

Hyundai Motor America, for instance, unveiled a turbocharged, four-cylinder engine with direct injection in Los Angeles for its six-passenger HED-5 concept car. Among U.S. manufacturers, Ford and GM are also increasingly using turbo-charging and direct injection to get more power out of smaller engines.

Better aerodynamics, innovative transmissions and lightweight materials can also help achieve better mileage, without having to rely on unproven technologies.

Here's a slideshow look at the "green" vehicles displayed in Los Angeles, ranging from the theoretical to the practical: