We interviewed officials in EPA’ s Office of Water; Office of Policy, Planning, and Evaluation; and all 10 of EPA’ s regional offices. On the bssis of these discussions and our literature review, we identified four projects in which pollutant trading has occurred or has been proposed. We then visited these four projectrs--the Dillon and Cherry Creek reservoirs in Colorado, the Tar-Pamlico River basin in North Carolina, and the Fox River in Wisconsin-and interviewed .