Petrol, diesel and its bio versions, ethanol either pure or in differing blends with petrol, possibly liquid hydrogen and an electric socket are all candidates to be essential fuel sources of the future.

All were being promoted under the pressure of concern about climate change and looming tougher emissions limits imposed by governments, especially in the European Union, one of the world's largest car markets.

"I suspect that we are going to get to a world that is not 98 percent gasoline or diesel powered -- I think that is going to change a lot," said Rick Wagoner, chief executive of General Motors, the world's largest carmaker.

"The game has been defined relatively narrowly -- in the US market it has been green equals hybrids. I think people are now waking up, it's a much broader playing field," he added.

However, the Swiss Green Party dismissed the array in Geneva as an "optical illusion" after carmakers missed EU emissions targets.

The Greens claimed that while the average fuel consumption of a car has been cut since 1990, the gains have largely been cancelled out by the fact that more people buy bigger and thirstier vehicles.

Alain Prost, a former world champion racing driver, who has been advising the French government on clean fuels, said he had sensed a slight retreat from the trend he saw at the Paris show in October.

Prost told Swiss television TSR that the industry was still torn between a growing conviction about impending environmental needs and its traditional marketing approach of wooing buyers with dream cars.

"We haven't cleared the hurdle yet. To a certain degree you could do both at the same time," Prost said.

Honda showed a concept of a small hybrid petrol-electric sports car that is meant to pump out less carbon dioxide than the tougher limits the EU is preparing for 2012, while maintaining the fun element that attracts younger buyers.

BMW was adamant that it would not lose its sporty aura with new efficient engines that switch off automatically while waiting at traffic lights and capture energy from braking systems.

"We're delivering proof of the fact that sheer driving pleasure and 'saving is fun' can go hand in hand. These engines provide higher performance at lower fuel consumption -- and thus lower emissions," said BMW Chairman Norbert Reithofer.

Like GM and DaimlerChrysler -- sometimes in joint projects -- BMW is also developing zero emissions hydrogen power.

"In the long term we see hydrogen as the solution," Reithofer said.

In the shorter term, GM and Ford were promoting ethanol produced from vegetable matter, which can be used on mildly modified petrol engines.

"Flexifuel technology is available today and it's affordable, not only for the environment, but also for the customer," said Ford of Europe chief executive John Fleming.

"Provided the fuel infrastructure continues to grow," he added. Ethanol pumps are only widely available in Brazil, Sweden and parts of the United States.

David Saldanha, head of European operations for Indian carmaker Tata, insisted that clean fuels would spread to emerging markets like India.

"There are a lot of programmes underway to use hybrid fuels. In India, pollution levels are high and everybody is keen, since the market is booming, that environmentally friendly fuel and other things happen."

More complex low emissions technology, however, is still costly even for giants like GM and Toyota.

"Right now this technology is expensive because the numbers are not high," Saldanha said, pointing to the cutaway model of a petrol-electric hybrid car for Toyota's luxury brand Lexus.

"But the moment it becomes a given, why wouldn't this car become as inexpensive as a normal petrol or diesel car?" he added, underlining the need for buyers.

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