Hollow Tree Energy Hollow Tree ENERGY
Team

We run these plants ourselves.

Our team has spent its careers inside power plants and power markets — operators, engineers, commercial traders, and investment professionals. That depth shapes what we buy, how we run it, and how we improve it.


Brad Romine

Brad Romine

Partner

Brad is a Founding Partner of HTE and a Partner at Ampliform, where he focuses on strategy and M&A.

From 2007 to 2020, Brad was a Managing Director at Castleton Commodities International (CCI). In this role, he was responsible for North American and European power research and for the build-out of the power asset business. Before CCI, Brad worked at Ritchie Capital and AEP.

Brad holds a Ph.D. in Management Science and Engineering from Stanford University and a B.A. from Cornell University.

Steve Culliton

Steve Culliton

Partner

Steve has over thirty years of trading and investment experience and is a founding partner at HTE.

Prior to HTE, Steve was a senior managing director at Castleton Commodities International (CCI) where he worked from 2007 to 2020. At CCI, he was responsible for the North American Power and Gas trading business and co-founded the North American Power investment business.

Before CCI, Steve was a portfolio manager at Citadel where he was an original member of the energy team. He spent five years at Williams Companies where he was Co-Head of Power Trading and Optimization.

He began his career at the CBOT as an options market maker.

John Vivenzio

John Vivenzio

Partner

John is a Founding Partner of HTE and a Partner at Ampliform, where he focuses on technology and enterprise platforms.

From 2009 to 2021, John was Chief Technology Officer at King Street Capital Management. In this role, he drove digital transformation across all business units within the firm. Before King Street, John worked at SAC Capital Advisors and in Bank of America's Prime Brokerage group.

John holds a B.S. from Penn State University.

Mikael Andren

Mikael Andren

Partner

Mikael is a Founding Partner of HTE and a Partner at Ampliform, where he focuses on platform strategy and investor relations.

Mikael is CEO and President of the Paul Tudor Jones II Family Office (JFO), where he works with its principals to manage the family's investments, real estate, and philanthropic activities. He helped lead the transaction to carve out Castleton Commodities International from Highbridge Capital and Louis Dreyfus. JFO was also a founding investor in Gore Street Energy, a leader in energy storage development in the UK and Ireland.

Mikael serves on the boards of the African Community and Conservation Foundation, the Pure Edge Foundation, and the Singita Grumeti Fund. He holds a B.S. from the University of Wisconsin-Madison and an MBA from Columbia University.

Brad Burmaster

Brad Burmaster

President

Brad is an operating partner at HTE and President of Gate City Power Holdings.

From 2006 to 2022, Brad led several asset and operational turnarounds for the infrastructure and clean energy businesses of Castleton Commodities International (CCI). Before joining CCI, Brad held numerous executive-level positions across the energy complex, including several COO and CFO roles. Brad holds a B.S. in Financial Management and Accounting from Oklahoma State University.

Sarah Finn

Sarah Finn

General Counsel

Sarah joined HTE as General Counsel in August 2025.

Before HTE, Sarah was Commodities Treasurer at Citadel, where she covered M&A and financing activities. Before Citadel, she spent eight years at Castleton Commodities International (CCI), where she led the Treasury function and worked closely with the partner group. Earlier in her career, Sarah was an Associate at Latham & Watkins, where she covered leveraged finance transactions.

Sarah holds a B.A. in Economics from Colgate University and a J.D. from Columbia Law School.