General Motors Corp. and ChevronTexaco Corp. announced October 24th that they had formed a pact to speed the pace of introducing petrol fuel cells into cars, a technology that cuts emissions of greenhouse gas carbon dioxide in half.

Fuel cells are seen as a likely successor to petrol-guzzling internal combustion engines. They produce electrical power from hydrogen and oxygen without combustion.

The technology can be fueled by hydrogen, or by fossil fuels such as petrol, which can then be converted into hydrogen. Pure hydrogen fuel cells emit only water vapor and no carbon dioxide.

"Car technology is changing, and we need to work to modify our fuels for use in fuel cell vehicles," said Gary Masada, president of ChevronTexaco's Energy Research and Technology Centre in a statement.

Neither ChevronTexaco nor GM would reveal the amount of money being spent on the "multi-year" project, or how many petrol fuel cell cars they expect to make.

GM has said it expects to be the first automaker to sell over a million cars and trucks run on fuel cells, but the technology will not be available for the masses until the end of the decade.