A recently developed theory that addresses bypass transition is used to study mechanisms responsible for transition in two-dimensional/axisymmetric e ows in conventional hypersonic wind tunnels. It is shown that transition in such facilities, where the intensity is in excess of 1%, is a result of a combined bypass/second-mode mechanism. This mechanism is validated by comparing predictions of the theory with heat transfer measurements carried out for straight and e ared sharp cones at zero angle of attack, a Mach number of 7.93, and unit Reynolds numbers of 1.6‐8.2 £ 10 6 /m. In general, good agreement with experiment is indicated. Nomenclature a = model constants (e rst-mode) a1‐a3 = model constants dee ned in Eq. (6) b = model constants (second-mode ) cπ = constant, 0.09 k = turbulent kinetic energy, m 2 /s 2 M = Mach number Q m = rms of mass e ux, kg/m 2 ¢s N m = mean mass e ux, kg/m 2 ¢s P = pressure, Pa qw = heat e ux at the wall, W/m 2 Re = Reynolds number