Closures for the drag and virtual mass forces acting on a single air bubble rising in initially quiescent pure water have been numerically investigated using direct numerical simulation techniques. A 3D Front Tracking model was used and the results were compared with simulation results obtained with a 2D Volume of Fluid model to assess the influence of the third dimension. In the simulations realistic values were taken for the physical properties, i.e., a density ratio of 800. The computed time-averaged terminal rise velocity and mean aspect ratio for individual air bubbles ranging in equivalent diameter from 1 to 10 mm rising in pure water compare well with available experimental data. © 2005 Elsevier Ltd. All rights reserved.