A new era of low crude prices and stricter regulations on climate change is pushing energy companies and resource-rich governments to confront the possibility that some fossil-fuel resources will remain in the ground indefinitely.

In a signal that the prospect is growing more likely, Exxon Mobil Corp. has said that as many as 3.6 billion barrels of oil that it planned to produce in Canada in the next few decades is no longer profitable to extract. A disclosure is expected in the coming week.

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