An in-depth numerical study has been carried out to investigate a high-pressure commercial scale (28 m diameter, 3040 m in height) slurry bubble column reactor. Typical superficial gas velocities are in the range of 0.53 m/s, and overall vapor holdups are in the range of 0.450.85. The study revealed that steady compartmental reaction models do not match plant data when reaction time constants are fast. Also, off-the-shelf commercial computational fluid dynamics codes do not produce useful information about a reactive column of this scale without first validating the model using data anchors from full-scale operational columns. Important measures include both transient and time-averaged profiles, integrals, and extrema of vapor holdup and reactants. Reactor designs based on this study show both improved productivity and product quality, allowing record production from existing plants along with substantial capital scope reduction for new plants. (c) 2011 American Institute of Chemical Engineers AIChE J, 2012