In this paper vane trailing-edge losses which occur in Organic Rankine Cycle (ORC) turbines are investigated. Experiments are performed to study the influence of dense gas effects on trailing-edge loss in supersonic flows using a novel Ludwieg tube facility for the study of dense-gas flows. The data is also used to validate a CFD flow solver. The computational simulations are then used to determine the contributions to loss from shocks and viscous effects which occur at the vane trailing-edge. The results show that dense gas effects play a vital role in the structure of the trailing-edge flow, and control the extent of shock and viscous losses.