A motorist's trip to the filling station is likely to be a complex business soon if the green marketing promises at the Geneva Motor Show, which opens on Thursday, are anything to go by.

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.