A novel methodology of on line measurement in an oscillatory baffled reactor (OBR) is presented. We show how the use of an electrical impedance tomography (EIT) sensor can map the spatial concentration of the dispersed phase in the emulsion and also obtain velocity profile information. Data are presented based on experimental work to enable production of water-in-oil/oil-in-water emulsions using the results of the on line measurement with the EIT. Process performance is quantified using dimensionless parameters of the OBR and the data obtained from cross-correlation of tomographic signals. The velocity results derived from the EIT data show good agreement with the well known flow pattern of the OBR described in previous works. The application of Maxwell relations enables the quantification of the local oil volume distribution in the emulsion process. Research demonstrates the principle how such methods can be used to monitor a chemical process in the OBR using electrical impedance tomography. (C) 2007 Elsevier B.V. All rights reserved.