Stirred tanks are used for several operations in industrial practice. Numerous scientific papers have been presented in literature dealing with experimental results on these applications. Comparisons and valuations of these data often fail because geometric parameters, experimental conditions, and measurement techniques differ notably. Therefore, it can be observed that correlations derived on the basis of these experiments often show large discrepancies. In a cooperative test of nine German working groups different experiments were carried out in stirred tanks under completely standardized conditions. Thereby, common measurement techniques were examined in their reliability.