Abstract: An effective means for flow visualization is the depiction of particle trajectories. When rendering large amounts of these pathlines, standard visualization techniques suffer from several weaknesses, ranging from ambiguous depth perception to high geometrical complexity and decreased interactivity. This paper addresses these problems by choosing a novel approach to pathline visualization in 3D space, which we call Virtual Tubelets. It employs billboarding techniques in combination with suitable textures to create the illusion of three-dimensional tubes, which efficiently depict the particles' trajectories, while still maintaining interactive frame rates. Certain issues concerning virtual environments and immersive displays with multiple projection screens are resolved by choosing an appropriate orientation for the billboards. The use of modern, programmable graphics hardware allows for an additional speed-up of the rendering process and a further improvement of the image quality. This results in a nearly perfect illusion of tubular geometry, including plausible intersections and consistent illumination with the rest of the scene. To prove the efficiency of our approach, rendering speed and visual quality of Virtual Tubelets and conventional, polygonal tube renderings are compared.