Three phase liquid-liquid-gas flow maps in pipes of medium inner diameters (5.6 mm and 7 mm), are presented. A low viscosity paraffin oil (4.5 x 10(-3) Pa s viscosity and 818.5 kg m(-3) density at 20 degrees C), deionised water and air are flowing concurrently in Schott Duran((R)) glass pipes. A decreasing pipe diameter changes the flow pattern maps and also the behavior of the transition boundaries. Flow patterns are determined by high speed photography. To illuminate the pipe, laser induced fluorescence (LIF) is applied. The laser sheet is cutting through the axial vertical plane of the pipe. The laser light excites a fluorescent dye (uranine) in the water phase to separate the phases optically. The resulting flow maps are compared with literature data and a theoretical model. (C) 2006 Elsevier Ltd. All rights reserved.