When Toyota wheeled out a futuristic Prius prototype in 1995 powered by a combination of petrol and electricity, many believed it would go the same way.

Twelve years later, its rivals are still trying to catch up and the hybrid will remain centre stage when the show gets under way again this week.

But the hybrid is not the only contender in the fuel efficiency race, with a host of environmentally-friendly technologies snapping at its heels.

Despite the success of the Prius, automakers are still hedging their bets on green technologies, with electricity, biofuels, clean diesel and fuel cells also seen as potential alternative power sources.

"The future is not just about hybrids," said Christopher Richter, an auto analyst at the investment bank CLSA.

"When I talk to automakers I sense a lot of uncertainty about what is going to be the dominant technology going forward," he said.

"Toyota has made a big push into hybrids, but other makers are looking at clean diesel. We're looking at a cocktail of different (technologies) that are going to be present, probably for the next few decades."

Japanese automakers are competing to be the first to launch low pollution diesel engines, which some analysts predict could eventually become more popular than petrol-electric hybrids due to their lower production cost.

And one day hybrids and clean diesel vehicles may come together.

"My guess is that in future actually many of the gasoline and diesel engines are going to be equipped with hybrid (technology). It's not really diesel against hybrid," said Credit Suisse auto analyst Koji Endo.

Nissan, which was slower than Toyota and Honda to embrace hybrids, plans to launch its first clean diesel engine vehicle in Japan in the second half of next year and will try to drum up interest in the technology at the motor show.

Richter at CLSA said diesel hybrid was "a very interesting possibility but still very costly."

Unsurprisingly, hybrids will dominate Toyota's stand at the show, which gets under way on Wednesday and opens to the public from Saturday.

Among them is the 1/X (pronounced one-Xth) plug-in hybrid, which Toyota says is two-thirds lighter than the Prius and twice as fuel efficient.

It can run on a mixture of gasoline and ethanol and uses rigid but lightweight carbon-fibre-reinforced plastic throughout the body frame.

Toyota will also show off a luxury hybrid sedan, a hybrid sports car and a new version of its one-seater, three-wheel i-swing "personal mobility machine," which caused a stir when it was unveiled two years ago.

Honda, which was the first automaker to introduce a hybrid in the US, will try to grab attention with its CR-Z lightweight hybrid sports car.

Nissan meanwhile will show off the latest version of its Pivo egg-shaped electric concept car with a cabin that can rotate 360 degrees.

The Pivo 2 can also drive sideways thanks to wheels that can turn 90 degrees for easy parallel parking and has a small "robot assistant" that can talk in English or Japanese to help with navigation or calm down angry drivers.

The dream of an electric car, which has been around since the time of Thomas Edison, has so far failed to break into the mainstream because of the high development cost and difficulties developing a suitable battery.

Automakers are also competing to develop lithium-ion rechargeable batteries suitable for long distance hybrids, but there are safety concerns after massive recalls by laptop computer manufacturers.

"Lithium-ion batteries can drive longer and are lighter. Nonetheless they have been tarnished because they do have a tendency to blow up," said Richter.

He said automakers were making intense efforts to perfect them.

Toyota in particular "has made a huge investment in hybrids and is going to want to have (a suitable lithium-ion battery) when these clean diesels start appearing in the market and posing a competitive threat to hybrids," he said.

Fuel cells, which run on hydrogen and emit only water, will also make an appearance at the event as Honda shows off the "PUYO" concept car, said to have a soft "gel body" to improve safety and "the feel of an adorable pet."

But it's not all about saving the planet: Nissan is building up the hype for the official launch of its all-new GT-R supercar, although pictures have already leaked onto the Internet despite its efforts to keep it under wraps.

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