The report by the advocacy group mirrors similar claims by Britain's leading scientific academy. Last September, The Royal Society wrote the oil company asking it to halt support for groups that "misrepresented the science of climate change."
Many scientists say carbon dioxide and other heat-trapping gases from tailpipes and smokestacks are warming the atmosphere like a greenhouse, melting Arctic sea ice and alpine glaciers and disturbing the lives of animals and plants.
ExxonMobil called the scientists' report Wednesday "yet another attempt to smear our name and confuse the discussion of the serious issue of CO2 emissions and global climate change."
ExxonMobil lists on its Web site nearly $133 million in 2005 contributions globally, including $6.8 million for "public information and policy research" distributed to more than 140 think tanks, universities, foundations, associations and other groups. Some of those have publicly disputed any link between greenhouse gas emissions and global warming.
Alden Meyer, the Union of Concerned Scientists' strategy and policy director, said in a teleconference that ExxonMobil based its tactics on those of tobacco companies, spreading uncertainty by misrepresenting peer-reviewed scientific studies or emphasizing only selected facts.
Dr. James McCarthy, a professor at Harvard University, said the company has sought to "create the illusion of a vigorous debate" about global warming.
The company said its financial support doesn't mean control over any group's views.
"We find some of them persuasive and enlightening, and some not," ExxonMobil spokesman Dave Gardner said. "But there is value in the debate they prompt if it can lead to better informed and more optimal public policy decisions."
He said the company believes that despite many scientific uncertainties, the risk that greenhouse gas emissions may have serious environmental effects justifies taking action to limit them.