As it turns out, BP's carbon dioxide reduction strategy -- achieved mostly through efficiency gains -- will save it about $650 million, said Mark Proegler, director of BP's Emissions Markets Group.

"That's a different concept -- I'm not sure we anticipated that," Proegler told Reuters in a telephone interview.

Energy efficiency measures helped BP reduce operational emissions by 10 percent between 1998 and 2001, Proegler said.

For example, BP cut flaring of unwanted natural gas at oilfields by the equivalent of 850,000 tonnes of greenhouse gases per year. BP also uses cogeneration -- or producing electricity from waste heat from refineries -- to boost its efficiency, he said.

BP is among some 12,000 industrial plants and businesses required to limit emissions beginning this year as part of European Union-wide rules to comply with the international Kyoto treaty. However, BP has been tracking its carbon emissions internally since 1998.

The Bush administration and Republican leaders in Congress oppose limiting US carbon dioxide emissions, preferring voluntary industry efforts. The United States is the biggest emitter of greenhouse gases, which are linked to a gradual rise in the earth's temperature.

"The application of a cap-and-trade program to (carbon dioxide) and other greenhouse gases would increase consumer energy costs, move American industry and jobs overseas and reduce economic growth," a White House spokeswoman said.

BP's Proegler said the United States needs to enact mandatory reduction targets to bring industry into sync with other markets.

Such mandates "are the right way to go with government setting the cap and providing the level playing field," he said.