As the United States grapples with the twin challenges of reducing dependence on foreign energy sources and reducing emissions of greenhouse gases, the topic of carbon dioxide (CO2) enhanced oil recovery (EOR) has received increased attention. In order to help inform the discussion, the Department of Energy’s National Energy Technology Laboratory has published this “primer” on the topic. Hopefully, this brief introduction to the physics of CO2 EOR, the fundamental engineering aspects of its application, and the economic basis on which it is implemented, will help all parties understand the role it can play in helping us meet both of the challenges mentioned above.