David Murphy is an Assistant Professor in the Geography Department at Northern Illinois University and an Associate of NIU's Institute for the Study of the Environment, Sustainability, and Energy. Dr. Murphy's research focuses on the intersection of energy, economics, and the environment. In his recent work, he has estimated how the extraction of natural gas in the Marcellus Shale has impacted the provision of ecosystem services. In addition to his work on ecosystem services, Dr. Murphy researches how the energy cost of energy production--the energy return on investment (EROI)-- differs between fossil fuels and renewable energy sources, as well as how EROI is related to structural changes in oil prices and economic growth. Dr. Murphy has published numerous peer-reviewed papers and book chapters, speaks regularly at academic conferences, and consults with the private sector on a variety of topics.