This represents a concern for various industrial systems, but especially for predicting the performance of safety systems in nuclear reactor systems. In order to remedy this gap in the current experimental database a series of experiments has been performed. These experiments included the measurement of the local interfacial area concentration and other parameters using local electrical conductivity probes in pipes with diameters of 0.152. m [6. in.], 0.203. m [8 in.] and 0.304. m [12 in.]. Volumetric fluxes ranged up to 2. m/s [6.56 ft/s] for the liquid phase and 10 m/s [32.8. ft/s] for the gas phase, and two nominal pressure conditions of 180. kPa [26.1 psia] and 280. kPa [40.6 psia] were included. Gas was injected as large cap bubbles in order to provide a basis for evaluating models for cap-bubbly flow at low void fractions. Measurements were performed simultaneously at three axial locations to allow the evaluation of interfacial area transport. The resulting data provides valuable insight into the flow structure and behavior in all flow regimes other than annular flow and will serve as a valuable database for the evaluation of models for predicting the transport of interfacial area across a wide variety of flow conditions and pipe sizes. © 2014 Elsevier Inc.