Oil–water–gas three-phase flows are frequently encountered in the chemical, nuclear, and petroleum industries. Due to the significant differences in physical properties of the three phases, the oil–water–gas flow structures are more complex compared with two-phase flows, which brings a great challenge to the flow parameter measurement of three-phase flows. In this study, a measurement system consisting of a conductance wire-mesh sensor (WMS) and distributed coaxial conductance sensors (CCSs) is designed to visualize the oil–water-gas flow structures. The distributed CCSs are used to monitor the conductance changes of the liquid phase and to realize the real-time correction of the gas-phase distribution obtained from the WMS. The measurement system can effectively avoid the influence of the nonconductive oil phase on the gas-phase visualization, and thus improve the accuracy of gas volume fraction measurement in oil-water-gas flows. The oil-water-gas flow structure and its evolution characteristics are studied according to the flow visualization and the probability density function (PDF) of the gas volume fraction. Notably, the effect of the dispersed oil phase on the Taylor bubble and the liquid slug is uncovered by investigating the local aerated characteristics of slug flows.