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William J O'Brien

William J O'Brien

Paul Weiss Rifkind Wharton & Garrison LLP1285 Avenue of the AmericasNew YorkNew YorkUSA10019-6064

Global Leader

Environment 2020

Professional Biography

WWL Ranking: Recommended

WWL says

William O'Brien ranks highly for his significant experience advising on the environmental impacts of investments into private and public companies.


William J O'Brien is counsel in the environmental law group and a member of the firm’s climate change working group. Bill has advised various private investment funds on the environmental aspects of investments in private and public companies and the acquisition of portfolio companies, including conventional and alternative energy companies. He has also advised on numerous financings and securities offerings. He has written and lectured on various aspects of environmental law, including environmental disclosure requirements in securities offerings, parent corporation liability for environmental obligations and environmental law aspects of real property transfers.

Chambers USA recognises Bill as a leading lawyer in transactional environmental law, with sources calling him “very business-focused and a great practitioner.” Bill has also been recognised by Super Lawyers and WWL for his work in environmental law.

Bill's recent representations include Elanco Animal Health Incorporated in its US$7.6 billion acquisition of the animal health business of Bayer AG; Salini Impregilo SpA in the US$555 million sale of the Plants & Paving division of its US subsidiary Lane Construction Inc to Eurovia SAS, a company of the Vinci Group; C&D Technologies, Inc, a portfolio company of KPS Capital Partners, LP, in its acquisition of Trojan Battery Company, LLC from Charlesbank Capital Partners, LLC and other shareholders; Honeywell, a Fortune 100 software-industrial company, in its spin-off of Garrett Motion Inc, Honeywell's former Transportation Systems business; Ingersoll-Rand plc in the merger of its industrial business with Gardner Denver Holdings, Inc, a provider of industrial equipment and technologies, creating a US$15 billion global leader in mission-critical flow and industrial technologies; KPS Capital Partners, LP in several matters, including in connection with its US$1.8 billion acquisition of Howden; and along with International Equipment Solutions, LLC, a portfolio company of KPS, in the US$690 million sale of the attachments division of International Equipment Solutions to Stanley Black & Decker, Inc; Bicent Power Company LLC, an affiliate of Beowulf Energy and Natural Gas Partners, in connection with an agreement to acquire Northwestern Corp’s 30 per cent interest in Colstrip Unit 4, a 740 MW coal-fired facility, for US$404 million in cash; Cenovus Energy Inc, a wholly-owned subsidiary of EnCana Corporation, in connection with Rule 144A/Regulation S offering of US$3.5 billion of senior notes; and Husky Energy Inc in connection with a public offering of US$1.5 billion of debt securities.

In addition, Bill has an active pro bono practice. He recently advised Green Chimneys Children's Services on its merger with Clearpool, Inc. He has also advised on a number of transactions for the Trust for Public Land, a nonprofit, land conservation organisation.

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