Similarity parameters are derived to correlate the selectivity of mixing controlled parallel reactions within stirred-tank reactors. For the case of laminar reactant feed, the Kolmogoroff time is shown to correlate selectivity in turbulent, semibatch reactors, provided the reactor Reynolds number Re < Re-C. The upper limit Re-C for the reactor Reynolds number is shown to be constrained by the volumetric flow ratio of reactant feed-to-pumping capacity. Moreover, for larger reactor Reynolds number Re > Re-C, the inertial time scale defined in terms of a reactor feed length is shown to correlate selectivity. Scaling laws are demonstrated from available tank data taken at up to three reactant feed points in both aqueous and viscous solutions, and for a range of vessel volumes, feed tube diameters, and feed times.