Private fortunes lead a $135m round in superhot-rock geothermal

On 17 September 2026, the Texas-based geothermal developer Mazama Energy announced an oversubscribed Series B of $135 million. The round was led by Centaurus Capital and Doerr Capital. ConocoPhillips and Shell Ventures took part, as did the existing investors Khosla Ventures and Gates Frontier. TechCrunch reported that SiteGround Capital, H. Barton Asset Management and the Jeffrey and Marieke Rothschild Foundation joined as new investors.

Canary Media described Centaurus Capital as the firm of the billionaire John Arnold, who said in the company’s release that superhot geothermal “offers the promise of firm, carbon-free power with a relatively small footprint”.

What the capital is for

The money funds Project Ceres, which has support from the US Department of Energy and involves drilling horizontally to show that a single well can deliver 15 megawatts of capacity. Mazama told Canary Media it expects to begin drilling later this year and to start testing early in 2027.

The company reported last October that it had built the hottest enhanced geothermal system on record, at 331°C, at its pilot site near the Newberry Volcano in Oregon. Its first well there reached 10,350 feet. The second reached the same depth roughly 80 per cent faster, which matters at rig costs that Canary Media put at more than $100,000 a day. Mazama now says the Oregon site could produce 10 gigawatts, against the 5 gigawatts its investor Vinod Khosla estimated a year ago, and that the first site should be complete by 2030 at 200 megawatts.

A round with an unusual shape

Two privately held investment firms led the round; a family foundation and several private asset managers followed; the corporate venture arms came in behind them. That ordering is the part worth noting. Pre-revenue drilling at these depths is not a natural fit for capital with a redemption calendar, and the investor list reflects it.

What it means for family offices

Deals of this kind test a family office’s governance before they test its judgement on the science. A single-asset, pre-revenue energy position that will not generate cash for several years needs a stated size limit, an agreed valuation policy between rounds, and a clear answer to who signs it off. Families that treat direct investing as an extension of the principal’s enthusiasm tend to discover those gaps late.

The presence of ConocoPhillips and Shell Ventures also cuts both ways. Strategic investors bring technical diligence that almost no family office can replicate in-house, which is part of the attraction of a club round. They also bring their own timetables and their own reasons for staying or leaving, and a minority co-investor inherits both. Advisers asked to review an allocation like this should be looking at the exit mechanics and information rights as closely as the geology.

For families already holding hydrocarbon wealth, next-generation geothermal has an obvious appeal: the drilling skills transfer, and the asset sits on the other side of the energy transition. That logic is sound as far as it goes. It is also how concentrated families end up with a portfolio correlated to the sector they were trying to diversify away from.

Sources: TechCrunch; Canary Media; OPB.