But a decade ago, respected commentators predicted there would be mass availability of fuel cell vehicles by 2005, he cautioned.

This had not yet materialised, although hundreds of prototype vehicles had been developed, Bentham told the 18th World Petroleum Congress.

The emergence of hydrogen as an energy carrier has particular relevance to South Africa, which has about three-quarters of the world's known global platinum reserves. Platinum is regarded as the most efficient catalyst in converting hydrogen to electricity.

German and Japanese car manufacturers are considered leaders in developing hydrogen fuel cell vehicles, among them Mercedes-Benz, BMW and Mazda.

These three manufacturers have plants in the country and strong links with the local automotive components industry, which is already involved in the beneficiation of platinum, particularly for catalytic converters.

Latest figures released by Trade and Investment SA revealed that catalytic converter exports were worth R8.1 billion and accounted for 38 percent of total automotive component exports of R21.3 billion in 2003.

But the congress heard that cost was a major factor inhibiting commercialisation, while further research and development were needed on production, storage, distribution and carbon capture.

Claude Mandil, the executive director of the International Energy Agency, said to make hydrogen cost effective as an energy carrier, the cost of producing it from primary energy sources would need to be cut by between three and 10 times.

Furthermore, the cost of fuel cells would need to decrease by between 50 and 100 times. "It's not impossible", said Mandil, but he believed it would take decades and a "tremendous amount of investment".

Ivar Hexeberg, the vice-president and head of hydrogen at Norsk Hydro, the Norwegian energy company, said in a "business as usual" scenario, it could take decades before hydrogen would become a significant energy carrier.

But an early technology breakthrough, or an unexpected event such as a war that was perceived to be linked to energy supplies, could speed up its development, said Hexeberg.

Hydrogen, the world's most abundant element, does not occur naturally as a gas on earth but is found in combination with other elements.

It can be produced from a variety of primary energy sources, including fossil fuels - coal, oil and gas - as well as nuclear and renewables. If harnessed from fossil fuels, resulting emissions of carbon dioxide would require carbon capture and storage.

Mandil said the energy agency believed carbon capture was "an absolute prerequisite" for the development of hydrogen as fossil fuels would probably be the most cost-effective source of producing hydrogen.

Most speakers at a round table on the hydrogen economy agreed that hydrogen should form an important part of the global fuel mix, along with cleaner traditional fuels, biofuels and gas to liquids.