The gas and particle flow patterns in computational models of swirl tube gas separators were simulated and compared with experiment, focussing on the presence and the effects of the end-of-the-vortex (EoV) phenomenon. It was found that for some swirl tube body lengths there are two possible stable positions of the vortex core depending on the inlet flowrate: a) centralized and following the swirl tube axis and b) bending to the swirl tube wall, which constitutes the EoV phenomenon, at a stable axial position. The computational results showed a good agreement with previous experimental observations of the EoV and they confirmed some specific features, which are typical for the EoV behaviour. Lagrangian simulations of the flow of particles in the swirl tube made it possible to visualize the particle motion and understand how the EoV phenomenon affects the behaviour of a single particle during separator operation and through this how the presence of an EoV affects separation efficiency of swirl tubes in general. (C) 2012 Elsevier B.V. All rights reserved.