We are the first to report pilot-scale experimental results on aeration efficiency of standard and newly developed cylindrical flow regulators (CVRs), conducted over a wide range of operational conditions, geometries and regulator types. In this work, two new (patented) constructions (CVR-2 and CVR-U) are introduced; they are aimed at enhancing reaeration capacity. They are compared with a standard cylindrical vortex regulator (CVR) optimised for flow control and throttling only. The aim of the study was also to understand the mechanisms that govern the aeration of vortex regulators. We have selected and studied the influence of key parameters on oxygen mass transfer in the vortex flow regulators in head-to-head comparisons. We prove that the reaeration capacity of CVRs is not linearly proportional to the number of active outlets, as multiple competing phenomena are responsible for the final aeration efficacy. We show that by changing the arrangement of the active outlets, it is possible to increase the aeration efficiency up to 20%. In the practical situations, this feature is beneficial in enhancing the aeration capacity of flow regulators and it does not degrade throttling properties. In order to allow practical application, the empirical formulas were developed to predict oxygen transfer efficiency. The investigations reported in this paper are expected to be transferable to other vortex regulators that exhibit similar flow hydrodynamics, especially those with a conical vortex chamber. (C) 2015 Elsevier B.V. All rights reserved.