Prepared by the Committee on Oxygen Transfer Standards of the Special Standards Division of the Environmental & Water Resources Institute of ASCEMeasurement of Oxygen Transfer in Clean Water, ASCE/EWRI 2-22, provides the latest methods for measuring the rate of oxygen transfer from diffused gas and mechanical oxygenation devices to water. This standard aims to be general enough to be applied to all clean water unsteady-state tests and specific enough to incorporate all essential procedures. This standard is an update of the 2006 version. Revisions to the mandatory requirements include use of the nonlinear least squares estimates for parameter fitting, the need to correct and report results to a common TSS level, and acceptance of a nitrogen gas method for deoxygenation. A new commentary provides a detailed description of a supersaturated oxygen desorption method. This method may be incorporated into a future revision of the standard as an acceptable method, pending a comparison of results with existing deoxygenation methods. ASCE 2-22 is meant to be used by engineers in the preparation of specifications for compliance testing by manufacturers developing performance information and is applicable to laboratory scale oxygenation devices with water volumes of a few gallons, as well as to full-scale systems with water volumes typical of those found in the activated sludge wastewater treatment process.