CO 2 outgassing from rivers is a critical component for evaluating riverine carbon cycle, but it is poorly quantified largely due to limited measurements and modeling of gas transfer velocity (k) in subtropical streams and rivers. We measured CO 2 flux rates, k and partial pressure ( p CO 2 ) in river networks of the Three Gorges Reservoir (TGR) region, a typical area in the upper Yangtze River with monsoonal climate and mountainous terrain. The observed k values (k 600 = 48.4 ± 53.2 cm/h) were showed large variability due to spatial variations in physical controls on surface water turbulence. Our k measurements using chambers were comparable with model derived velocities. Unlike in open waters, k is more pertinent to flow velocity and water depth in the studied small rivers. Our results show that TGR river networks emitted approx. 1.4 Tg CO 2 /y using varying approaches such as chambers, measured k and developed k model. This study suggests that incorporating scale-appropriate k measurements into extensive p CO 2 investigation is required to refine basin-wide carbon budgets in the subtropical streams and small rivers. We concluded that simple parameterization of k as a function of morphological characteristics was site specific and hence highly variable. k models should be developed for stream studies to evaluate the contribution of these regions to atmospheric CO 2 .