Experimental work has examined the fluid dynamics of immiscible liquid-liquid flow inside a narrow channel reactor. Results have shown that stable parallel flow, ideal for rapid mass transfer between the phases, can be achieved over a range of flow rates and viscosities. Further experiments were conducted to examine the performance of a narrow bore capillary reactor for the nitration of benzene which requires rapid mass transfer to achieve efficient low by-product output. Results have shown that industrially competitive reaction rates can be achieved from a relatively simple reactor design with modest bore sizes of between 127 mu m and 254 mu m.