Water and energy are inexorably linked--energy is needed to pump, treat, and transport water and large quantities of water are needed to support the development of energy. However, both water and energy may face serious constraints as demand for these vital resources continues to rise. Two examples that demonstrate the link between water and energy are the cultivation and conversion of feedstocks, such as corn, switchgrass, and algae, into biofuels; and the production of electricity by thermoelectric power plants, which rely on large quantities of water for cooling during electricity generation. At the request of this committee, GAO has undertaken three ongoing studies focusing on the water-energy nexus related to (1) biofuels and water, (2) thermoelectric power plants and water, and (3) oil shale and water. For this testimony, GAO is providing key themes that have emerged from its work to date on the research and development and data needs with regard to the production of biofuels and electricity and their linkage with water. GAO's work on oil shale is in its preliminary stages and further information will be available on this aspect of the energy-water nexus later this year.