Billionaire Family Offices Back Geothermal Startup Mazama Energy

In September, family offices executed 42 direct investments, down from 52 the month before, according to data from Fintrx. Five of those deals targeted clean-energy companies, highlighting a continued appetite for climate-focused ventures despite an overall slowdown. Among the clean-energy bets, John Arnold’s Centaurus Capital and John Doerr’s family office co-led a $135 million Series B round for Mazama Energy, a geothermal startup. Bill Gates’ private venture capital firm also participated in the financing.

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Family offices—investment entities tied to ultra-wealthy families—have been shifting toward larger, later-stage rounds while reducing the total number of checks. Recent mega-rounds include a $500 million Series A for Fab2 and a $250 million Series D for Precision Neuroscience, both involving prominent family offices. The September activity underscores that, even as the volume of deals contracts, capital continues to flow into high-impact sectors such as clean energy.

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Mazama Energy’s approach drills into extremely hot rock and circulates water through engineered fractures to extract heat for carbon-free electricity. In 2025, the company’s Oregon pilot site reached 629 °F, which Mazama claims is the hottest engineered geothermal system on record. The firm asserts the pilot can already generate 10 gigawatts of power, positioning the technology as an engineering solution rather than a scientific unknown.

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Mazama CEO Sriram Vasantharajan said the Oregon proof-of-concept demonstrates a clear path to commercialization and helped attract top investors. He emphasized that investors seek a proven track record and that Mazama has moved beyond platform creation to real-world application. Vasantharajan also noted that geothermal projects differ from many deep-tech investments because they do not require long-term horizons; the heat resource is already proven.

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• “When you talk about family offices or even any other investor, what they look for is a demonstrated track record. It's one thing to create the tech platform, but what Mazama has done is actually applied it,” — Sriram Vasantharajan, mazama CEO

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