A single-use, stirred tank bioreactor designed for the non-GMP cultivation of mammalian cell lines. Its rigid design includes a semi-hemispherical shaped polycarbonate vessel, a multi-port high-density polyethylene (HDPE) headplate, a scoping marine impeller, both open pipe and sintered spargers, weldable C-Flex tubing, and all necessary gas inlet and outlet filters. Because the vessel is molded component, additional ports were added below the minimum working volume level including, one luer actuated sample port, one liquid inlet/outlet port, two liquid addition lines, direct sparging lines and a harvest line. All gas and liquid addition ports located below the minimum working volume incorporate check valves to ensure uni-directional flow of gas or liquid. The CellReady 3L Bioreactor is preassembled, gamma irradiated and shipped ready to use.