The discharge characteristics of orifices at low pressure ratios were investigated. Probe measurements of high-velocity jets confirm and extend the work of Stanton. Expansion factors (Y) at pressure ratios down to r = 0.13 were measured for the flow of air in a 2-in. pipe meter and for the flow of steam in a 3-in. pipe meter. Both meters were installed in accordance with ASME specifications, and operated at a diameter ratio of 0.15. The effects of high approach velocity on the discharge characteristics of square-edged orifices at low pressure ratios were investigated; expansion factors were determined for diameter ratios from 0.2 to 0.8 over a range of pressure ratios from unity to 0.2. A linear Y-r correlation is shown to exist at low pressure ratios; a change of flow regime occurs at a pressure ratio of 0.63. A theoretical solution for supercritical flow, previously established by the author, is further compared with experimental results.