Separation caused by the pressure rise induced by flares has been experimentally investigated in the Mach number range of 1.5 to 5.0 and in the Reynolds number range (based on boundary-layer thickness) of 1.5X104 to 12X104. The purpose of the investigation was to determine the model geometry and flow conditions for which separation can be expected for a turbulent boundary layer of zero pressure gradient on the cylinder approaching the flare. Comparisons are made of the boundary-layer-separation characteristics of these three-dimensional flares with two-dimensional separation results from a previous investigation.