The current profile loss prediction methods for axial turbine blades predict a monotonic increase in profile losses at outlet Mach numbers above 1.0. However, linear cascade testing in the literature has revealed a more complex behaviour. An objective of this investigation was to help clarify the flow features that are most influential on the profile losses in the transonic and supersonic regimes. Four linear cascades of turbine blades were investigated both experimentally and computationally. Linear cascade measurements were carried out using the High Speed Wind Tunnel (HSWT) at Carleton University. It was found that the base pressure was strongly linked to the profile losses in the transonic and supersonic regimes. The position of the trailing edge shock impingement on the adjacent blade and its associated effect on the boundary layer were also found to influence the profile losses.