In this work, hydrodynamics of contaminated bubble swarms is numerically investigated using the free surface cell model combined with the spherical stagnant cap model. The governing field equations are solved numerically to elucidate the effect of Reynolds number, gas holdup and degree of contamination on the hydrodynamic behavior of bubble swarms. New extensive results are reported over the range of conditions as follows: Reynolds number, Re: 1-200, bubble holdup, Phi: 0.1-0.5, and stagnant cap angle, alpha: 0-180 degrees. Finally, the effects of these parameters on streamlines and vorticity contours, surface pressure and vorticity distributions and on drag coefficients are discussed in detail. Briefly, the drag coefficients decrease with the decreasing stagnant cap angle and/or the decreasing bubble hold up and/or the increasing Reynolds number; whereas the ratio of the pressure and friction drag coefficients exhibits mixed trends with respect to these parameters. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.