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X-ray computed tomography (CT) is used to explore the differences in gas dispersion in a gas-sparged stirred-tank reactor (STR) for different operating conditions. X-ray CT imaging is completed for various impeller speeds and gas flow rates in a 0.21 m ID STR made out of acrylic and equipped with a nylon Rushton-type impeller. From the CT slices, major differences in local time-averaged gas holdup can be seen, depending on the operating condition. Completely dispersed conditions have a relatively uniform holdup profile while flooded conditions have an increase in gas holdup towards the center of the tank. The high resolution of the X-ray system allows for visualizing time-averaged gas flow details such as low gas holdup regions directly above the impeller region under certain operating conditions and recirculation regions behind the baffles.