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Hydrogen is, says the US Department of Energy, "America's clean energy choice". It could be the fuel that the world runs on, once the oil has run out.

Â鶹Éç Environment Correspondent Richard Black visits a number of laboratories around the USA and Europe where the issues of making the hydrogen, storing it and then distributing it are being tackled.

Are Hydrogen Fuel Cells as efficient an energy carrier as we are told? Or do the dangers and costs override the potential?

This is the second of a four-part Discovery series, "Fuelling the Future".

Listen here (Real)

First broadcast: Wednesday, 22 February, 2006 at 1006 GMT