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Why have some estimates of undiscovered technically recoverable oil or gas changed so much from previous estimates?

Petroleum geologists have long known that oil and gas resources were present in “tight” or impermeable formations such as shale. But there was no feasible way to extract that oil and gas, so they were not “technically recoverable” and were not included in USGS assessment results.

Thanks to new technologies, oil and gas can now be extracted from “tight” formations, so they can be counted in assessments of undiscovered technically recoverable resources.

Learn more: USGS Energy Assessments

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