While the diesel market is proving popular in Europe, executives at the Geneva Motor Show say that ultimately fuel cell vehicles or electric cars will triumph.
Hybrid cars, fuel cell models and diesel vehicles have been on prominent display at the show, but experts such as Honda's Laurent Aebi - who has been showcasing the FCX fuel cell car - said it was an interim period.
"Diesel is popular in Europe, clearly, but it's a short-term trend," he told MSNBC.
"I give it another ten years maximum. After that it will be the hybrid car. But both the diesel car and hybrid car are a transition as we head to fuel cell cars or pure electric cars."
Demand for green cars in the UK and Europe is increasing steadily at present, with carmakers announcing higher sales and higher targets this week.
Toyota has announced that it is raising its 2005 European goal for sales of its Prius hybrid model to 20,000 units, a 5,000 increase on the previous target.
Toyota's luxury brand Lexus, meanwhile, has almost sold its entire allocation of 4x4 hybrids in the UK.