Abstract: GPU-based ray casting, as introduced by Krüger and Westermann [2003], is an effective method for volumetric rendering. Unfortunately, conventional methods of Empty Space Skipping (ESS) using spatial partitioning, which accelerate ray casting by culling ray-surface intersection tests in empty parts of the volume, do not align well with GPU architectures. CPUs are usually required for tree generation and parsing, as well as the data transfer from CPU to GPU. Such CPU-based pre-processing is time-consuming, with the result that spatial tree structures are invariably applied to static datasets.