A key comparison between seven national metrology institutes in the area of low-pressure gas flow was organized by the Comit? International des Poids et Mesures (CIPM) and the Working Group for Fluid Flow. A set of eight critical flow venturis with dedicated, redundant pressure and temperature sensors was used as the transfer standard at flows between 4.4 g/min and 260 g/min. Preliminary testing in the pilot lab determined temperature operating bounds and corresponding uncertainties. The transfer standard contributed a standard uncertainty of <0.026% to the comparison, primarily due to environmental temperature effects, the pressure sensors, and gas properties (the critical flow function and molecular mass of moist air). Redundant measurements by the transfer standard and the star pattern testing were valuable for maintaining low transfer standard uncertainty. The results supported equivalence between the labs with the largest difference between any two participants at any of the flows tested being 0.308%. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).