The phenomenon of the geothermal gradient refers to the rate at which the temperature within the Earth's crust rises as one drills deeper into the ground. An increase of 30°C per kilometer is the average value for the Earth's continental crust, although this can vary significantly by region (depending on local geology).

The depth required to reach temperatures of 500°C depends primarily on the local geothermal gradient. In exceptionally active geothermal regions such as Iceland or any other volcanically active areas like Oregon (USA), temperatures around 500°C can occur at only 3-5 km depth. IDDP, for example, has identified 500°C as a target at approximately 4-5 km in the Hengill and Krafla areas.

In regions with a lower geothermal gradient, substantially deeper drilling is required. This is the fundamental challenge Endoria seeks to address: bringing SuperHot Geothermal Energy to locations where naturally accessible high-temperature resources do not exist.
 

Above approximately 374°C and 221 bar, water enters its supercritical state. At these conditions, the energy density and power-generation potential of geothermal resources increase dramatically compared with conventional geothermal systems.