A comprehensive literature search was conducted to obtain the holdup data for different gases in various liquids and slurries using bubble and slurry bubble column reactors operating under wide ranges of conditions in different size reactors provided with a variety of gas spargers. The data were used to develop two novel correlations, one for the total gas holdup and the other for the holdup of large gas bubbles. The total gas holdup correlation is capable of predicting the experimental data within an absolute average relative error (AARE) and standard deviation (a) of 20%, whereas the correlation of the holdup of large bubbles is capable of predicting the experimental values within AARE and a of about 25 and 27%, respectively. The novel correlations were used to predict the effects of pressure, temperature, gas velocity, solid concentration, rector size, and distributor type on the holdup of syngas (H-2/CO = 2) in various slurry bubble column reactors (SBCRs) operating under typical Fischer-Tropsch conditions. (c) 2005 Elsevier B.V.. All rights reserved.