In order to evaluate the separation efficiency and flow field of deoiling hydrocyclones a three dimensional simulation is performed using large eddy simulation (LES) approach. Although this approach has been used in other types of hydrocyclones, the present work is a primer application of the LES approach for simulation of deoiling hydrocyclones. Due to anisotropic behavior of flow inside the hydrocyclones. LES is a suitable method to predict the flow field since it resolves large scales and models isotropic small scales. Obtained velocity field using the LES approach in comparison with other turbulence models is in good agreement with available experimental velocity measurements. The method of Lagrangian particle tracking with an optimized search algorithm (closest cell) is also used to evaluate the separation efficiency of deoiling hydrocyclones. Special attention is drawn to droplet drag coefficient, while the differences between separation efficiency curves using modified drag coefficient are also highlighted. (C) 2012 Elsevier B.V. All rights reserved.