The interaction between kinetics and mass-transfer effects is determined by the flow regime in liquid-liquid multiphase microreactors. The operating conditions under which the various flow regimes Such as slug flow and stratified flow Occur ill liquid-liquid systems has not been extensively Studied and is not well-Understood. The effect of operating conditions oil slug length for instance is not well-known. The present study focuses oil microreactors fabricated in Perspex (poly(methyl methaacrylate) (PMMA)), which are essentially microchannels with a rectangular cross-section. Experiments are carried Out for a wide range of flow rates, channel sizes, and fluid systems with varying properties. Two different kinds of flow regimes, slug flow and stratified flow, are experimentally observed, and these are predicted Using numerical Simulations. We divide the space of operating conditions (the two liquid flow rates) into different regions such that in each region the now regime is distinct. The dependence of Slug length on flow rates and other parameters such as channel size, Viscosity, Surface tension, and contact angle have been determined and are quantitatively compared with predictions of simulations.