ESDU 72011 provides information on the total-pressure loss and static-pressure recovery for incompressible and subsonic compressible fluid flow through sudden enlargements of area in ducts. Data are given for the subsonic flow of liquids and gases through near symmetrical enlargements with area ratios between 0 and 1 and at Reynolds numbers@ based on upstream pipe diameter@ greater than 20. The effects of various non-uniform upstream velocity profiles are considered for incompressible flow. Worked examples are provided.