In October 1999, the “International Committee of Weights and Measures” (CIPM) reached — within the scope of the Metre Convention — the agreement on the shape “Mutual Recognition Arrangement” (MRA) of the national standards and of the associated measurement capabilities of the “National Metrology Institutes” (NMI). Objectives of this agreement are the determination of the “Degree of Equivalence” (DoE) between the individual national standards, the mutual recognition of certificates of the NMIs and an increase in the transparency of measurement results. Among the confidence-building measures for the implementation of the MRA, international interlaboratory comparisons (CIPM “Key Comparisons”, KC) between the NMIs play an elementary role. Within the scope of this contribution, comparison measurements of the coherent SI unit volume — especially of ‘volumes of water’ — between the worldwide renowned flowrate standard measuring system of PTB´s Berlin Institute (“Heat Meter Test Section”, WZP), of PTB Braunschweig (“Hydrodynamic Test Field”, HDP) and of the flowrate laboratory of the Federal Office for Metrology and Survey (“Bundesamt für Eich- und Vermessungswesen”, BEV) in Vienna are presented. In addition, fundamental procedures for comparison measurements between flowrate standard measuring facilities are shown in this contribution and results of these measurements for 20°C are presented as examples.