There will be room for diesel engines and gasoline-electric hybrids to co-exist in the future, an industry insider has stated.

John Geis, an engineer at Ford, told the Detroit Free Press, that diesels enjoy political backing in Europe, while Japan favours hybrids due to their superior performance in stop-start driving conditions common in crowded Japanese cities.

Diesel-fuel taxes in Europe are lower than gasoline taxes in an attempt to encourage the use of diesel as it is more efficient than gasoline. However, diesels are deemed too dirty for use in densely populated Japan cities.

Mr Geis added that both have opportunities to thrive in the US.

"There are going to be niches for both. It will depend on how you drive," he stated.

However, Larry Burns vice president for advanced research at GM suggested that in the long-term hydrogen fuel cells will become the technology of choice.

The results of a JD Power and Associates survey suggest that clean diesel engines are also likely to prove more popular than hybrids in the US if the costs were equivalent.

Indeed, three quarters of today's gasoline-engine owners say they would consider a diesel if the cost was the same, against only 59 per cent for hybrids.

Those buying diesel tend too keep their cars longer, however, as they update their models less quickly than other owners.

Engine comparison of hybrid and diesel models suggests that the diesel engine is more fuel-efficient, but that this is reversed when driving in the city.

Some experts argue that the ideal fuel economy would be based on a combination of an electric motor, a powerful battery and a diesel engine, but it is widely acknowledged that such an unwieldy mix would be unlikely to be commercially viable.