Hydrodynamic characteristics of countercurrent two-phase flow in vertical and inclined channels are investigated. Experiments are performed using air and water at room temperature (25 to 27° C) and 160-kPa pressure, in a 208-cm-long, transparent, tubular test section with a 1.9-cm inner diameter. Tests are systematically performed with downward liquid superficial velocities and upward gas superficial velocities covering the 0 to 10 and 0 to 150 cm/s ranges, respectively, with 0-, 8-, 28-, 45-, and 60-deg angles of inclination with respect to the vertical line. Experimental flow regime maps are provided for all the aforementioned angles of inclination. For the vertical channel configuration, the obtained data are compared with existing data and flow regime transition models. Test section average void fractions are found to be sensitive to the channel angle of inclination. For the vertical channel configuration, the data are compared with the previously published data and empirical correlations.