The Thermo Scientific™ HyPerforma™ Single-Use Fermentor (S.U.F.) has been purposefully engineered to best match traditional stirred tank reactor (STR) design features. The S.U.F. delivers performance equivalent to that of stainless steel steam-in-place/clean-in-place (SIP/CIP) reactors for research- and pilot-scale microbial bioproduction at both 30 L and 300 L liquid working volumes. However, due to the implementation of single-use film wall, sparge, and agitation, there can be limitations when moving aggressively growing, dense cultures from steel tanks to single-use reactors. To characterize the limitations of available single-use bioreactors, a rigorous comparison was undertaken in collaboration with multiple vendors. To evaluate the oxygen transfer coefficient (kLa), a procedure with a 10 g/L sodium chloride (NaCI) solution and single-use optical dissolved oxygen (DO) probes was used in all vessels to obtain comparable results. The various reactors were tested at preset maximum rpm and air flow rates without any oxygen supplementation allowed. The results were supplied to reactor vendors without disclosing the suppliers’ names. Here we present the performance of 30 L and 300 L S.U.F.s in comparison to other unnamed vendor options.