Oil shale deposits in Colorado, Utah, and Wyoming are estimated to contain up to 3 trillion barrels of oil--or an amount equal to the world's proven oil reserves. About 72 percent of this oil shale is located beneath federal lands managed by the Department of the Interior's Bureau of Land Management, making the federal government a key player in its potential development. Extracting this oil is expected to require substantial amounts of water and could impact groundwater and surface water. GAO's testimony is based on its October 2010 report on the impacts of oil shale development (GAO-11-35). This testimony summarizes (1) what is known about the potential impacts of oil shale development on surface water and groundwater, (2) what is known about the amount of water that may be needed for commercial oil shale development, (3) the extent to which water will likely be available for such development and its source, and (4) federal research efforts to address impacts to water resources from commercial oil shale development. For its October 2010 report, GAO reviewed studies and interviewed water experts, officials from federal and state agencies, and oil shale industry representatives.