The "big three" US car producers have said that they are to double their estimates of how many renewable-energy vehicles they will have produce by 2010.

Ford, General Motors and DaimlerChrysler are targeting a range of alternative fuel methods in order to hit the combined target.

In a letter written to the US Congress, bosses from the three firms said that they would use a range of hybrid, ethanol and other bio-fuel engines.

"We need business and government to work together to enhance the production, distribution and use of renewable bio-fuels," the chief executives said.

"Our hope is that with this commitment, fuel providers will have even more incentive to produce ethanol and other biofuels and install pumps to distribute them."

Platinum catalysts are used in hybrid fuel technology.

The US Supreme Court recently said it would consider whether or not the country should introduce measures limiting the amount of carbon dioxide released into the atmosphere in an attempt to tackle climate change.

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