Specifications for geothermal resource classification have been updated in 2022 as part of the United Nations Framework Classification (UNFC) for Resources.

A presentation on the 2022 UNECE (2nd Edition) update was given by Graeme Beardsmore to the Western Pacific Branch of the IGA
(URL to presentation)

More details on UNECE / UNFC can be found at https://unece.org/sustainable-energy/sustainable-resource-management/unfc-and-geothermal-energy