CO2 will be captured from a steam-producing boiler at the ageing Lacq gas field in an experiment to test the feasibility and costs of carbon storage, it said.

Instead of being released into the atmosphere and adding to the global-warming effect caused by carbon pollution, the CO2 will be injected 4,500 metres (14,625 feet) below ground in a now-empty gas field.

Carbon storage is being closely studied by big greenhouse-gas polluters.

Several pilot schemes are already underway in Europe and the United States, exploring different techniques in different geological formations.

Environmentalists caution that storage may carry long-term risks.

If the underground chamber subsides or is ruptured by an earthquake, that would disgorge the CO2 into the atmosphere, worsening the greenhouse effect at a stroke for future generations, they say.

Jean-Michel Gires, Total's director for sustainable development and the environment, said the engineering phase of the Lacq scheme was already completed.

If all goes well, the site would start storing CO2 from November 2008, with the goal of sequestering up to 150,000 tonnes over the following two years.

"We will be monitoring how it unfolds over two years. It has to be completely reliable," Gires said.

Total, on its website, says it has allocated 50 million euros (65 million dollars) for the Lacq project and other technologies to reduce carbon emissions.

To capture the CO2, the site will use oxycombustion, the first time this method will be tried in an "integrated" site, meaning the location where the carbon pollution is produced and then stored.

Carbon storage carries a significant economic cost, which Total estimates at between 60 and 100 euros (80 and 130 dollars) a tonne. This is many times the commercial cost of buying carbon to offset one's own pollution.

Carbon on the European market has crashed to less than 1.50 euro (1.95 dollars) a tonne, compared with roughly 26 euros (33.8 dollars) a year ago, driven down by problems of excessive quota allocations among European countries bound by the Kyoto Protocol's pollution limits.

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