A fully liquid-thermostatted micro-reactor probe head for H-1 NMR spectroscopic studies of fast reaction kinetics, which was recently developed, is tested in the present work by studying fast esterification kinetics in the stopped flow mode. It is shown that reliable kinetic data can be obtained using this set-up for reactions with time constants down to a few seconds. The two test systems are the formation of methyl acetate (MA) and methyl formate (MF). Both are homogeneously catalyzed by sulfuric acid, which is added to the educts in different amounts. The temperatures of the kinetic studies are chosen between 303 and 333 K. The reaction kinetic data for both systems is correlated by activity-based kinetic models. For the MA formation, reference data from the literature is available, however only for regimes with time constants of minutes to hours. That data fits well to the results of the present study. The MF formation was studied here at conditions in which the time constants are of the order of seconds and therefore no reference data is available. The new probe head substantially extends the range in which NMR spectroscopy can be used for studies of fast reaction kinetics. (C) 2016 Elsevier B.V. All rights reserved.