A large fraction of the organic carbon derived from land that is transported through inland waters is decomposed along river systems and emitted to the atmosphere as carbon dioxide (CO 2 ). The Amazon River outgasses nearly as much CO 2 as the rainforest sequesters on an annual basis, representing ∼25% of global CO 2 emissions from inland waters. However, current estimates of CO 2 outgassing from the Amazon basin are based on a conservative upscaling of measurements made in the central Amazon, meaning both basin and global scale budgets are likely underestimated. The lower Amazon River, from Óbidos to the river mouth, represents ∼13% of the total drainage basin area, and is not included in current basin-scale estimates. Here, we assessed the concentration and evasion rate of CO 2 along the lower Amazon River corridor and its major tributaries, the Tapajós and Xingu Rivers. Evasive CO 2 fluxes were directly measured using floating chambers and gas transfer coefficients (k 600 ) were calculated for different hydrological seasons. Temporal variations in pCO 2 and CO 2 emissions were similar to previous observations throughout the Amazon (e.g., peak concentrations at high water) and CO 2 outgassing was lower in the clearwater tributaries compared to the mainstem. However, k 600 -values were higher than previously reported upstream likely due to the generally windier conditions, turbulence caused by tidal forces, and an amplification of these factors in the wider channels with a longer fetch. We estimate that the lower Amazon River mainstem emits 0.2 Pg C year −1 within our study boundaries, or as much as 0.48 Pg C year −1 if the entire spatial extent to the geographical mouth is considered. Including these values with updated basin scale estimates and estimates of CO 2 outgassing from small streams we estimate that the Amazon running waters outgasses as much as 1.39 Pg C year −1 , increasing the global emissions from inland waters by 43% for a total of 2.9 Pg C year −1 . These results highlight a large missing gap in basin-scale carbon budgets along the complete continuum of the Amazon River, and likely most other large river systems, that could drastically alter global scale carbon budgets.