Volumetric liquid-side interphase mass transfer coefficients were experimentally measured in vertical channels supporting cocurrent, upward two-phase flows. Deionized water and an aqueous solution of sucrose constituted the liquid phase, pure nitrogen was the gas phase, and oxygen was the transferred species. In each test, oxygen concentrations in the liquid at two measurement stations near the two ends of the test section were measured on-line. The channel entrance effects were eliminated by performing hydrodynamically-identical tests with two different test section lengths, and using the shorter test section results for quantification of entrance effects in the longer test section. The channel average gas holdups representing developed flows were also measured using two simultaneous, quick-closing valves. The obtained data were compared with predictions of several widely-referenced correlations, with significant disagreements among the correlations, and between the correlations and the data. New empirical correlations were developed based on the obtained data representing the fully-developed slug and churn flow regimes.