Sheila Slocum Hollis has played a key role in the formation and implementation of energy law and policy in the United States. She began her energy law career as a trial lawyer at the Federal Power Commission from 1974 to 1976, serving as lead counsel on the Pennzoil-United spinoff case, going on to serve twice in federal government.
In 1977, she became the first director of the office of enforcement of the Federal Energy Regulatory Commission, establishing the office and its policies and procedures, which remain in place today. As a professorial lecturer in law at George Washington University School of Law, she has taught energy law for 20 years to over 600 students in the environmental and energy law program and was recently recognised by the school for her teaching contribution.
Hollis is widely published in energy law and policy matters, having co-authored two energy law texts and numerous articles on energy policy, enforcement and regulation in the natural gas, independent power and cogeneration, nuclear and hydroelectric areas, along with related environmental topics.

After joining Duane Morris, she became the founding practice group leader for the firm's energy, environment and resources practice group. Her daily work focuses on the areas of energy transactional and regulatory law and international and administrative law before government agencies, Congress, state and federal courts, and other entities. She also practices on domestic and international energy, water and environmental matters, representing governmental bodies, the power and natural gas industries, and other entities.

Hollis has a long and venerable career representing clients in matters relating to infrastructure, natural gas and oil development, transportation and distribution, energy reliability, enforcement and compliance, and international energy policy.