We release an updated inventory of what we consider drilled but uncompleted wells (DUCs) each month in our Drilling Productivity Report (DPR). We publish updates to DUC estimates by region in a publicly accessible spreadsheet. In May 2021, the most recent month available, we estimated that the United States has about 6,521 DUCs in seven major tight oil and shale natural gas basins, up from about 4,425 DUCs in 2013, the earliest year in the data series. Nearly 40% of DUCs (or 2,616 DUCs) are in the Permian Basin, located in western Texas and eastern New Mexico.