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Dennis M. O'Leary



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Admitted to the Ontario Bar: 1984

Dennis O'Leary is a partner and a member of the firm's Litigation Group and Mining Group. Dennis is also a Co-Chair of the firm's Energy Team, and a member of the Environmental and Transportation Teams.


Dennis practises in the areas of energy and environmental, transportation, regulation, insurance and commercial litigation. He has appeared before all levels of the courts and numerous administrative tribunals in respect of a broad range of regulatory and litigation matters, many of which involved significant energy, environmental and transportation law matters.  

On the energy side, Dennis provides advice and acts as counsel on a wide range of issues, including the Ontario Energy Board in respect of divisional court appeals, as co-counsel to board staff at several rate and facilities hearings and assisting board staff with the development of the draft codes for use in Ontario's deregulated electricity sector. He acted as the facilitator at the board mandated settlement conference held as part of an application by one of Ontario's major utilities for approval of its rates. Dennis has appeared before the National Energy Board in respect of toll and facilities hearings. He provides legal advice to international utilities on the regulation of electricity and natural gas at both the federal and provincial levels.  

His environmental experience includes acting for clients with respect to applications for landfills and other waste facilities, responding to spills and other discharges of contaminants, commencing or defending civil lawsuits and defending environmental prosecutions. Dennis has acted as counsel to significant parties in several large environmental assessments, including the Timber Management Class Environmental Assessments and the Ontario Hydro Supply/Demand hearing. 

From a transportation law perspective, Dennis advises clients in respect to freight and warehouse claims, the defence of personal injury claims and how to meet the requirements of the Transportation of Dangerous Goods Act and Regulations. He has represented transportation clients in respect of regulatory offences and in regard to general commercial litigation. Dennis has also assisted transportation clients involved in commercial transactions from an environmental, regulatory and litigation perspective.

Dennis' clients include national and international companies, organizations, insurers, financial institutions and individuals. Dennis has also successfully acted for many clients making use of alternative dispute resolution formats.

Special DesignationsRecommended in The Legal 500 Canada for his expertise in the practice areas of Energy: Power and Environment

MembershipsAssociation of Power Producers of Ontario
The Advocates' Society
Canadian/Ontario Bar Association (Environmental Law Section, Past Executive 1990-2001)
Canadian Transport Lawyers Association (CTLA)
Transportation Lawyers Association

Professional Activities

Counsel to Enbridge Gas Distribution Inc. for Demand Side Measures (DSM) matters, including appearing at the DSM Generic Proceeding and annual account clearances.

City of Toronto Contaminated Lands Task Force, 1995-1997

Member of the legislative sub-committee of the CBA(O) Environmental Section examining and contributing to several submissions made to the Ministry of the Environment and Energy in respect of amendments to environmental legislation in Ontario, October 1994-1997

Member of the Lynn McLeod Strategic Environmental Policy Working Group, December 1994 to the spring of 1995 which developed the environmental platform for the 1995 general provincial election

Chair of the CBA(O) Environmental Law Executives' Subcommittee and contributor to the Submission to the Government of Ontario in respect of the proposed amendments to the Statutory Powers Procedure Act, November 1994

Proposed Amendments to the Trees Act - A Submission to the Ministry of Natural Resources, July 1992


LL.B., Queen's University, 1982
B.A., University of Toronto, 1979

*Practising as a professional corporation