Although steam-in-place (SIP) is the primary process for sterilization of bioreactors, sterilization guidelines do not exist for equipment design and little quantitative data are available concerning critical parameters such as length, diameter, and orientation of deadlegs. This study correlated microbiological sterilization data with the critical dimensionless parameters governing buoyancy driven convective flow within dead-ended tubes during SIP sterilization. These parameters were shown to be the overall Grashof number, Gr(OV), and aspect ratio, Ar. Typical values of Gr(OV) for bioprocess equipment can range from 10(3) to 10(5), while Ar may, vary from near 0 to 20 during sterilization of vertical tubes at 121 degrees C. Reproducible sterilization resulting in a 12 log reduction in B. stearothermophilus spores required an Ar of less than 7 when Gr(OV) was 0.7 x 10(5), whereas an Ar of 12 could be used when Gr(OV) was 2.8 x 10(5).