US geothermal developer Mazama Energy has raised $135 million in new capital to advance commercial development of superhot rock geothermal systems, including a Series B financing led by Centaurus Capital and Doerr Capital.
The financing includes investment from ConocoPhillips and Shell Ventures, alongside repeat backing from Khosla Ventures and Gates Frontier. Other participants include SiteGround Capital, H. Barton Asset Management and the Jeffrey and Marieke Rothschild Foundation.
Mazama is developing geothermal systems at temperatures well above those typically associated with conventional geothermal resources. At its Newberry site in Oregon, the company created an engineered geothermal system in 2025 at 629°F (331°C), which it describes as the highest-temperature EGS yet developed.
The company is now drilling a second well, Project Athena, at the same site. Mazama said the well reached a depth of 10,350 feet in 15 days, approximately 80% faster than its 2025 well, and is being extended towards rock temperatures of about 750°F (400°C).
At these temperatures, water approaches supercritical conditions, potentially allowing substantially greater energy extraction from each well. Mazama estimates that a 750°F resource could produce up to 10 times the power of a conventional 390°F (200°C) well, although commercial performance remains to be demonstrated.
The company is targeting reduced well numbers and water use as a result of the higher energy density. It estimates that its approach could require 80% fewer wells and 75% less water than conventional geothermal developments.
Part of the new funding will support Project Ceres, a US Department of Energy-backed programme intended to advance horizontal wells in superhot rock. Mazama is targeting 15 MW of generation capacity per well and plans to demonstrate power production in 2027.
The projects address three technical challenges central to superhot geothermal: drilling and operating equipment at extreme temperatures, creating a productive engineered reservoir, and extracting heat reliably enough for sustained electricity generation.
Mazama is also evaluating other sites in the US and internationally, while targeting more than 10 GW of independently certified resource potential at Newberry. The company’s longer-term objective is to develop superhot geothermal as a source of firm electricity using a smaller surface footprint than some conventional generation technologies.
