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Patrick Day

Of Counsel

2515 Warren Avenue, Suite 450, Cheyenne, WY 82001

Patrick defends energy companies, utilities, pipelines, refiners, and other businesses in state and federal litigation, and specializes in challenges to state and federal regulations. 

He represents energy companies in environmental litigation in state and federal courts around the country as well as before state agencies. Patrick is also one of Wyoming’s most experienced appellate specialists, arguing cases around the country. Energy companies engage Patrick when faced with high stakes litigation. Clients trust his advocacy skills to achieve positive results when their businesses are on the line. When not in the courtroom, Patrick also works as an arbitrator or mediator.


Patrick is currently involved in the legal challenges to EPA’s Clean Power Plan and is working with utilities in their efforts to comply with the Clean Air Act’s Regional Haze Program. Patrick also coordinates legal teams working on refinery accidents and mineral development conflicts. With almost 35 years of experience, Patrick knows where to turn for legal and consulting expertise within Holland & Hart and throughout the country, often assisting clients with unusual technical challenges by assembling and managing the resources to work on the problem.

Client Results

  • Argued before the U.S. Court of Appeals, District of Columbia Circuit, on behalf of a coalition of industry groups challenging EPA's endangerment rule, which has triggered an avalanche of national regulations addressing greenhouse emissions. Coalition for Responsible Regulation v. EPA, Nos. 09-1322, 10-1092, 10-1073, 10-1167, Jul. 26, 2012. Patrick is also involved in the pending challenges to EPA’s Clean Power Plan, and co-authored one of the Stay Motions in those cases granted by the U.S. Supreme Court.

  • Williston Basin Interstate Pipeline Co. v. An Exclusive Gas Storage Leasehold and Easement in the Cloverly Subterranean Geological Formation, et. al., 524.F.3d 1090 (9th Cir. 2008), represented client in complex litigation involving natural gas storage and production.

  • Represented numerous energy clients over several decades, shaping Wyoming’s severance and ad valorem tax valuation systems. Wyoming Dept. of Revenue v. Exxon Mobil Corp., 162 P.3d 515 (Wyo. 2007) Wyoming Min Ass'n v. State, 748 P.2d 718 (Wyo. 1988) (No. 87-128).

  • Powder River Basin Resource Council v. Wyoming Dept. of Environmental Quality, 226 P.3d 809 (Wyo. 2010). Defended one of the nation’s last air permits for a coal fired power station in Wyoming.

  • Mutual of Omaha Ins. Co. v. Blury-Losolla, 952 P.2d 1117 (Wyo. 1998) (No. 96-304) Established the governing law on class action jurisdiction in Wyoming.

  • Rocky Mountain Oil and Gas Ass'n v. State Bd. Of Equalization, 749 P.2d 221 (Wyo. 1987) (No. 87-194) Had Wyoming’s property tax system declared unconstitutional. 

  • Fiscus v. Atlantic Richfield Co., 742 P. 2d 198 (Wyo. 1987) (No. 87-47) Established the governing law on parent/subsidiary tort liability.



Speaking Engagements


Bar Admissions

Court Admissions


  • Chambers USA: America’s Leading Lawyers for Business, Litigation: General Commercial, Senior Statespeople 
  • Benchmark Litigation, Local Litigation Star, 2013-2021
  • The Best Lawyers in America©, Commercial Litigation, 2003-2022; Litigation – Environmental, 2003-2022
  • Mountain States Super Lawyers®, Top 100 Lawyers, 2021
  • Mountain States Super Lawyers®, Energy & Resources, 2009-2010; 2013-2021

Professional and Civic Affiliations

  • Current President, Equal Justice Wyoming, Wyoming’s first state sponsored legal aid organization
  • Wyoming Affiliate of the American Diabetes Association, Past Chair
  • Board of Directors, Cheyenne School Foundation, Past Chair

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