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Thomas Sansonetti


555 17th Street, Suite 3200, Denver, CO 80202
505 9th St. NW, Suite 700, Washington, DC 20004
2515 Warren Avenue, Suite 450, Cheyenne, WY 82001

A longtime litigator and project team leader, Tom helps clients permit and develop projects with potential obstacles in mind.

Long before a lawsuit can threaten a project, he counsels clients on how to develop effective plans of action that will meet government environmental permitting requirements and stand up to judicial scrutiny when those clients' projects are challenged in court.

Tom joined Holland & Hart in 1993 and built a nationally recognized practice in natural resources and environmental law. Considered an expert in natural resources and environmental matters, Tom served as an Assistant Attorney General for the Environment and Natural Resources Division in the Department of Justice and as the Solicitor and Associate Solicitor for Energy and Resources at the Department of the Interior. He has argued before the U.S. Supreme Court and in seven Federal Circuit Courts of Appeal, and served as a federal prosecutor in environmental crimes cases. Tom’s appellate experience highlights his ability to argue cases at all levels of the federal court system.

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Experience in many areas of energy and natural resources law, including:

  • American Indian law
  • Appeals of adverse federal agency decisions before the Interior Board of Land Appeals and Interior Board of Indian Appeals
  • Clean Air Act and Clean Water Act issues
  • Development of renewable energy projects, including geothermal, solar, and wind projects
  • Endangered Species Act
  • Oil and natural gas permitting
  • Permitting of oil and natural gas pipelines and electric transmission, including right-of-ways
  • Public lands management
  • Surface mining development and reclamation
  • Water rights

Client Results

Energy and Natural Resources Projects
  • Team leader for permitting natural gas pipeline through four states and 680 miles.
  • Represented a regional natural gas pipeline operator in negotiations with tribes to purchase a major natural gas pipeline.
  • Represented various companies in obtaining rights-of way over state, federal, and tribal lands.

  • Represented an international geothermal company in their negotiations to place a project on an American Indian reservation.
  • Represented a company in the negotiation with an American Indian tribe for the construction of a natural gas plant on an American Indian reservation.
  • Represented a major national resource company in obtaining the permit to construct a dam and hydropower facility.
  • Represented a public utility in the negotiations with an American Indian tribe to explore for coal on the Indian reservation.

Environmental Litigation
  • Defended the state and federal permits granted to a major U.S. natural gas company for the construction of a natural gas pipeline in the 9th Circuit Court of Appeals.
  • Represented a major U.S. natural gas pipeline operation in suing the federal government over the clean-up of uranium tailings on an American Indian reservation.
  • Represented a major U.S. natural gas pipeline operation in defending a class action lawsuit brought by individual tribal members claiming the amount of right-of-way lease payments were deficient.
  • Part of a litigation team that successfully represented Pennsylvania Power and Light before the United States Supreme Court in overturning a Montana Supreme Court decision concerning the ownership of riverbeds within the state.
  • Represented a public utility in negotiations with an American Indian tribe to explore for coal on the tribe’s reservation.

Representation of Clients before Federal and State Agencies and Congress
  • Represented a regional public utility before the EPA on issues relating to the Clean Air Act.

  • Represented trona and coal companies on regulatory matters before the Department of the Interior.
  • Represented various entities in dealing with the intricacies of the Indian Regulatory Gaming Act and the Bureau of Indian Affairs.
  • Represented both companies and ranchers on clarifying their water rights in western states.
  • Represented a large charitable trust health group in obtaining funding to improve and increase FDA inspections for imported foods.



Speaking Engagements


Bar Admissions

Court Admissions


  • Chambers USA, Native American Law, Senior Statespeople, Nationwide, 2012-2022
  • American College of Environmental Lawyers, Fellow, 2012-Present
  • The Best Lawyers in America© Lawyer of the Year, Environmental Law – Cheyenne, 2016, 2021
  • The Best Lawyers in America© Lawyer of the Year, Government Relations Practice – Cheyenne, 2012, 2015, 2017
  • The Best Lawyers in America©, Environmental Law, Government Relations Practice, 2007-2023; Native American Law, 2016-2023; Oil and Gas Law, 2018-2023
  • Mountain States Super Lawyers®, Energy & Resources, 2011-2022
  • Mountain States Super Lawyers®, "Top 100 Lawyers," 2018
  • Denver Business Journal, Who’s Who in Energy, 2012-2013

Professional and Civic Affiliations

  • Washington & Lee University School of Law, Member, Law Council, 2011-2019
  • University of Denver Sturm College of Law, Natural Resources Law, 2012 Practitioner in Residence
  • United States Commission on Civil Rights for the State of Wyoming, Chairman, 2008-2012
  • Republican National Committee, General Counsel, 2001
  • Wyoming's Republican National Committeeman, 1996-2001
  • Wyoming Republican Party, Chairman, 1983-1987

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