A New York judge sided with Exxon Mobil on Tuesday in a closely-watched environmental case, concluding the oil giant did not mislead investors in its climate change disclosures.

The ruling by Barry Ostrager, a judge in the New York state court, rejected arguments by the state's attorney general that the company duped investors by downplaying the costs of mitigating climate change.

The decision came after a trial that included testimony from former Exxon Mobil CEO Rex Tillerson and focused on granular questions of accounting at a company that has long been a lightening rod for environmentalists.

In a sweeping 55-page ruling, Ostrager wrote that Exxon Mobil employees called by New York to bolster its case were "uniformly favorable to Exxon Mobil" and that employee witnesses were "comprehensive and meticulous" in their work.

Ostrager rejected the state's contention that discrepancies between Exxon Mobil's public and internal estimates of the cost of potential climate mitigation stemmed from fraud.

"The court finds that the Office of the Attorney General failed to prove by a preponderance of the evidence that ExxonMobil made any material misrepresentation" of significance, Ostrager wrote.

New York Attorney General Letitia James, who inherited the case from two predecessors, struck a defiant tone in defeat.

"For the first time in history, ExxonMobil was compelled to answer publicly for their internal decisions that misled investors," James said in a statement that said the state had shown a pattern of "materially false, misleading and confusing" company representations about climate change.

"We will continue to fight to ensure companies are held responsible for actions that undermine and jeapordize the financial health and safety of Americans across our country, and we will continue to fight to end climate change."

An Exxon Mobil spokeswoman said the ruling "affirms the position ExxonMobil has held throughout the New York Attorney General's baseless investigation."

The oil giant "provided our investors with accurate information on the risks of climate change" and would continue to invest in "breakthrough technologies to reduce emissions while meeting society's growing demand for energy," she said.

A judge in New York has ruled that Exxon Mobil did not mislead investors in its climate change disclosures
A judge in New York has ruled that Exxon Mobil did not mislead investors in its climate change disclosures AFP / ERIC PIERMONT

The decision came after a trial that heard from a dozen witnesses and marked the culmination of a three and a half year probe into Exxon Mobil's system for estimating future climate costs in energy projects and for communicating to the public about climate change.

Tillerson, who served as US President Donald Trump's first secretary of state after leading the oil giant from 2007 through 2016, testified that the company's use of two different forecasts for greenhouse gas costs was for planning purposes and not intended to deceive investors.

Prosecutors argued that Exxon Mobil's use of the lower of the two forecasts misled investors about the cost of climate mitigation and the risk that some assets could become "stranded" or uneconomic produce because of aggressive climate mitigation policies.

New York had argued that damages could amount to as much as $1.6 billion for investors.

But Ostrager concluded that Exxon Mobil's system was sound and that variance between estimated costs were justifiable based on a complex series of factors, including the possibility that greenhouse gases mitigation would be more costly in some markets than others.

Ostrager further wrote that Exxon Mobil public reports cited by New York were not misleading to investors.

Exxon Mobil continues to face similar cases in other state and federal courts.

Ostrager, who called the New York claims "hyperbolic," said his decision turned on questions of securities law rather than the environment.

"Nothing in this opinion is intended to absolve ExxonMobil from responsibility for contributing to climate change through the emission of greenhouse gases in the production of fossil fuel products," Ostrager wrote.