The real-time cross-sectional distributions of the gas holdups in gas-liquid and gas-liquid-solid systems are measured using electrical capacitance tomography. For the gas-liquid system, air as the gas phase and both Norpar 15 (paraffin) and Paratherm as the liquid phases are used. Polystyrene beads whose permittivity is similar to that of Paratherm are used as the solid phase in the gas-liquid-solid system. The three-phase system is essentially a dielectrically two-phase system enabling measurement of the gas holdup in the gas-liquid-solid system independent of the other two phases. A new reconstruction algorithm based on a modified Hopfield dynamic neural network optimization technique developed by the authors is used to reconstruct the tomographic data to obtain the cross-sectional distribution of the gas holdup. The real-time flow structure and bubbles flow behavior in the two- and three-phase systems are discussed along with the effects of the gas velocity and the solid particles.