  The ratio between the photon spectrum in B -> X_s gamma and the differential
semileptonic rate wrt the hadronic variable M_X/E_X is a short-distance
quantity calculable in perturbation theory and independent of the Fermi motion
of the b quark in the B meson. We present a NLO analysis of this ratio and show
how it can be used to determine |V_ub/V_cb| independently of any model for the
shape function. We also discuss how this relation can be used to test the
validity of the shape-function theory on the data.
