Abstract Background and Aims The study of intradialytic oxygen saturation (SO2) in hemodialysis (HD) patients is a significant yet under-explored area. This study's objective was to evaluate the epidemiological aspects of SO2 during HD. Method SO2 levels during HD were measured using the Crit-Line Monitor (CLM; Fresenius Medical Care North America, Waltham, MA), a device certified by the US Food and Drug Administration (FDA) for the measurement of hematocrit and SO2 in the extracorporeal circuit. CLM measurements were recorded at 10-second intervals and transmitted into Amazon Web Services (AWS) via Apache KAFKA, a real time streaming software. Apache KAFKA was rolled out in phased approach, started early 2021. We extracted CLM data between January 14, 2021, and July 30, 2023. CLM values with the following characteristics were deemed implausible and hence, excluded: SO2 ≤ 0 or ≥99.9; hematocrit < 15% or >60%. We computed basic statistics of SO2 for every HD session. We then excluded the sessions with the standard deviation of SO2 < 0.1%, an interquartile range of zero, and sessions with less than 360 SO2 measurements (i.e., less than 60 minutes of recording). Results We collected data from over 5.6 million HD sessions. After data cleaning, we retained 4.9 million HD sessions from 72,656 patients treated in 727 dialysis clinics across the US. The average duration of a session was 204.5 (±42.8) minutes. Per HD session, on average 1,227 (±257) SO2 measurements were recorded. The distribution of the number of SO2 measurements per HD session is shown in Fig. 1A. The mean of the session-level average SO2 was 88% (±15%). The distribution of session-level average SO2 is shown in Fig. 1B. The bimodal distribution of SO2 is attributed to the use of arterio-venous and central venous vascular accesses, respectively. Conclusion We collected and analysed a substantial dataset of intradialytic SO2 in a large US HD population. These data provide a rich source for future research into SO2 and its clinical correlates. Exploring intradialytic SO2 in depth will offer valuable insights to improve patient care and optimize treatment procedures.