In this paper, overall gas holdup is investigated experimentally for a helium gas at 90 degrees C injected through a slurry of water at 22 degrees C and alumina solid particles in a slurry bubble column reactor. This work examines the effects of superficial gas velocity, static liquid height, solid particles concentration and solid particle diameter, on the overall gas holdup of the SBCR. These effects are formulated in forms of empirical equations. From the experimental work, it is found that the overall gas holdup increases by increasing the superficial gas velocity with a higher rate of increase at lower superficial gas velocity. In addition, the overall gas holdup decreases by increasing the static liquid height and/or the solid concentration at any given superficial gas velocity. Moreover, at a higher solid concentration, the changing rate of the overall gas holdup with the superficial gas velocity and/or the solid concentration is lower. Furthermore, it is observed that the effect of the solid particle diameter on overall gas holdup is negligible. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.