Eurostar, the passenger train service linking London and mainland Europe, set a target on Tuesday to cut CO2 emissions by 25% per passenger by 2012.
Eurostar said it would make the cut by sourcing power from greener electricity generators, increasing train capacity and improving the efficiency of its rolling stock.
Where Eurostar cannot eliminate CO2 emissions, it will invest in carbon offsetting schemes, it added.
Carbon offsetting allows companies to buy carbon credits from other firms or countries that have reduced emissions.
"Unlike other transport operators, who ask passengers to volunteer to offset CO2 emissions at their own expense, we will bear the cost of making every journey carbon neutral. We will not charge a penny extra," said Eurostar chief executive Richard Brown.
"We do know that a high-speed rail journey is 10 times greener than flying," he added.
Eurostar was owned, when launched, by France's SNCF railway body, Belgium's SNCB and British Rail. The British interests are now held by Eurostar UK (EUKL).
SNCF and SNCB are responsible for the running of Eurostar services on their own territory.
On the British side this is done by the ICRR consortium, which comprises the National Express Group, which has a 40% stake, SNCF with 35%, SNCB with 15% and British Airways with 10%.