An experimental investigation is reported on the effect of fiber length distribution on gas holdup in a cocurrent air-water-fiber bubble column. Different combinations of 1 and 3mm Rayon fibers are used to simulate different fiber length distributions. At a constant total fiber mass fraction, gas holdup generally decreases with increasing mass fraction of the 3mm Rayon fiber while other conditions remain constant. Crowding factors estimated using four different methods (N-c = N-c,N-A, N*(c), N-c,N-L, and N-c,N-M) and the parameters (Nc,LNf0.2)-N-0.8 and N-c,M(N,f)0.8(0.2) are tested on their performance to quantify the overall effects of fiber mass fraction and fiber length and its distribution on gas holdup. (Nc,LNf0.2)-N-0.8 and (Nc,MNf0.2)-N-0.8 provide the best characterization of the fiber effects on gas holdup in the cocurrent air-water-fiber bubble column. The crowding factor estimated using the model-based average fiber length (N-c,N-M) also provides a good characterization and is better than the other crowding factor definitions. (c) 2006 Elsevier Ltd. All rights reserved.