Microscale processes offer a substantial advantage to the process industry as separation is conducted rapidly and efficiently. However, the effectiveness of the separation depends on the stability of the flow regime. Experimental and numerical analysis was carried out to characterize the flow patterns of polyethylene glycol 200 (PEG200) and diesel fuel at several flow ratios in order to achieve optimal conditions for a stable pattern. Computational fluid dynamics (CFD) was employed using the volume-of-fluid (VOF) model and the results were validated with the experimental data. Both experimental and numerical outcomes revealed two-phase flow patterns. These findings enable the application of the simulated module for further liquid-liquid mass transfer studies where sulfuric compounds exist as solutes in the fuel.