A chemical method has been used to quantify the effective interfacial area in a baffled continuous stirred liquid-liquid reactor. Two and four straight paddle impellers were used in the experimental runs, at 34degreesC, with hold-up fractions of dispersed organic phase between 0.061 and 0.166 and stirring speed ranging from 3 60 to 1500 rpm. Influence of the residence time on the formation of the interfacial area generated in this system was not registered; however, differences were reported between continuous and batch mode operations.The interfacial area was correlated to hold-up fraction and Weber number by a new empirical model proposed in this work. This model allows to use only one equation to calculate the interfacial area in this continuous stirred reactor in the wide range of operating conditions tested (490 < We < 9600), which include different flow regimes. This is a relevant contribution as previous studies in this field only contemplate turbulent flow. In the transitional regime the mean drop size diameter decreases abruptly with Weber number, but this pattern changes in the higher range of Weber where the dispersed drops become smaller very smoothly. This pattern does not depend on the agitator used or hold-up fraction. The mean drop size diameter is smaller for the four paddle impeller and increases with hold-up fraction. The model developed may be applicable to dispersions in aromatic nitration reactors, improving its operation and design. (C) 2003 Elsevier Ltd. All rights reserved.