Bioreactors are disclosed that include a vessel, a jet mixing system comprising a plurality of jet flow agitators disposed in the vessel, each jet flow agitator comprising a shaft, a shroud surrounding the shaft, the shaft having a bore and a plurality of orifices in communication with the bore, and an impeller mounted on the shaft within the shroud, and a gas delivery system configured to supply a process gas to the vessel through the bore such that the gas exits the orifices. The vessel may include a vent, and the gas delivery system may include a source of oxygen in communication with the vessel, an oxygen monitor configured to monitor the oxygen content of a liquid in the vessel, and a controller configured to adjust the oxygen content of the liquid, using the vent and oxygen source, in response to input from the oxygen monitor.