HOUSTON -- The opening of an investigation of Exxon Mobil by the New York attorney general's office into the company's record on climate change may well spur legal inquiries into other oil companies, according to legal and climate experts, although successful prosecutions are far from assured.
Many oil companies have funded lobbying efforts and research on climate change, so prosecutors would most likely be able to search through vast amounts of material. The industry has also resisted pressure for years from environmental groups to warn investors of the risks that stricter limits on carbon emissions could have on their businesses, although that appears to be changing.
"Exxon Mobil is not alone," said Stephen Zamora, a professor at the University of Houston Law Center. "This is not likely to be an isolated matter."
Energy experts said prosecutors may decide to investigate companies that chose to fund or join organizations that questioned climate science or policies designed to address the problem, such as the Global Climate Coalition and the American Legislative Exchange Council, to see if discrepancies exist between the companies' public and private statements.
British Petroleum (now BP), Shell Oil, Texaco (now part of Chevron) and Exxon, along with several manufacturing companies, were all members of the coalition, a group of companies and trade associations that started an advertising campaign in the 1990s opposing Washington's involvement in strong international efforts like the Kyoto Protocol initiative to reduce greenhouse gas emissions.
Energy experts said internal documents from member companies about climate change could contradict what the companies said as part of the coalition, which disbanded in 2002.
"There was a concerted effort by multiple U.S. oil companies to obscure the emerging climate science consensus throughout the 1990s," said Paul Bledsoe, a former White House aide to President Bill Clinton on climate issues. "This group may be vulnerable to legal challenge."
British Petroleum and Shell Oil left the coalition early on, setting a pattern in which European oil companies took a very different course on climate and other environmental issues than most of their U.S. competitors.
Shell announced this summer that it would not renew its membership in the American Legislative Exchange Council, or ALEC, a free-enterprise group that has opposed government mandates, subsidies and other efforts to force or encourage companies to develop and use more renewable energy sources.
Occidental Petroleum and several other companies have also left ALEC, but Chevron and Exxon Mobil still support the group.
Big U.S. and European oil companies can point to efforts they have made to support renewable energy, perhaps clouding attempts by prosecutors to paint them as one-sided on the issue of climate change.
Chevron, for example, has been a pioneer in geothermal energy for decades. Exxon Mobil has a project underway to convert algae into a biofuel that can run vehicles and soak up carbon. BP is active in wind power. Several companies in the United States have begun working with the Environmental Defense Fund to limit emissions of methane.
"The oil and gas industry has probably been the biggest funder of research into decarbonization, maybe more even than the federal government," said Michael Webber, deputy director of the Energy Institute at the University of Texas.
But it has been foreign oil and gas companies, including most recently Total of France and BHP Billiton of Australia, that have been most outspoken about the dangers of climate change.
Last month, 10 of the world's biggest oil companies, including BP, Royal Dutch Shell, Saudi Aramco, Repsol of Spain, Eni of Italy and Total, made a public declaration acknowledging that their industry must help address global climate change.
None of the big U.S. companies joined the group, largely because they oppose carbon taxes and trading of carbon-emission permits — remedies that would raise the price of fossil fuels like oil and natural gas.
Last September, five major European, Asian and Latin American oil and gas companies signed on to a voluntary U.N.-backed program to monitor and disclose methane emissions, as well as invest in technologies to control greenhouse gases from their operations.
The only U.S. company to join was Southwestern Energy, a midsize Houston-based company that mostly invests in natural gas.
"There are times to go off the reservation, and this may be one of them," said Steven L. Mueller, chief executive of Southwestern Energy, just after his company joined the effort.
Energy experts say it will be harder to make cases against the oil companies than it was against tobacco companies that deliberately hid research from their customers, since many oil company scientists, including those of Exxon Mobil, have presented papers on climate change publicly at conferences and contributed to the research of international groups concerned with the issue.
"Unless they directly lied in Congress, the legal case against them is kind of thin," said Hal Harvey, chief of Energy Innovation, an energy consultancy. But he added, the record shows that the companies "have walked away from being a credible spokesman on science."