How can electromagnetic radiation heat oil shale underground?

Volumetric heating is an in situ method used to extract oil from oil shale by applying electromagnetic radiation or electric current directly to the underground rock formation.1

This process functions similarly to a microwave oven, where the emitted radiation excites the molecules within the rock, causing them to generate heat internally. By heating the rock volumetrically, the process facilitates the pyrolysis of kerogen—the organic matter trapped within the shale—which breaks chemical bonds to release liquid and gaseous hydrocarbons. Unlike methods that rely on conduction or the circulation of hot gases, volumetric heating targets the rock mass itself, offering a specialized approach for in situ recovery.1