It has become popular to argue that American energy security and climate change challenges can be solved by a series of win-win policies that tackle both problems at once. A look at the future of the Canadian oil sands calls that belief into question. Exploiting the oil sands would boost the worlds supply of liquid fuels from outside the volatile Middle Eastbut could simultaneously spur significant increases in global greenhouse gas emissions. Oil sands supporters argue that, given the close relationship between the United States and Canada, the security benefits should trump climate concerns. Yet many advocates of aggressive action on climate change strongly oppose oil sands development.