The mixing performances of five anchor coaxial mixers (anchor-Scaba 6SRGT, anchor-Rushton, anchor-Spiral, anchor-ARI, and anchor-A200), utilized for the agitation of non-Newtonian fluids, were evaluated in the laminar and transitional regime. To achieve this goal, power consumption and mixing time were measured as a function of the design parameters. An electrical resistance tomography (ERT) system was used to measure the mixing time. The non-Newtonian fluid was 2.0% xanthan gum solution (pseudoplastic fluid possessing yield stress). It was found that for all five configurations there was a critical speed ratio (R-N = central impeller speed/anchor speed), which beyond it the mixing time did not decrease anymore with an increase in the speed ratio. Prior to this critical speed ratio, mixing time was proportional to R-N(0.4) regardless of the coaxial mixer configurations. The new correlations developed for the generalized Reynolds and power numbers of the coaxial mixers were tested successfully for all studied configurations. The power consumption and the mixing time data revealed that the Scaba-anchor coaxial mixer in the co-rotating mode was the most efficient mixer among the coaxial mixers explored in this study. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.