  We use the perturbative QCD methods of Lepage and Brodsky to calculate the
rate for B-bar_s -> rho K_s, with an eye toward the CP violating unitarity
triangle angle gamma. We show that, although the penguins are large, there are
regions of the allowed parameter space of the Cabibbo-Kobayashi-Maskawa mixing
matrix wherein gamma is measurable in the sense that penguins change the value
of sin(2gamma) one would extract from the attendant time dependent asymmetry
measurement by less than 29 per cent, so that a 3sigma measurement of
sin(2gamma) as being different from 0 is allowed by the corresponding
theoretical uncertainty. This would establish CP violation in B_s decays. The
rates which we find tend to favor the type of luminosities now envisioned for
hadron-based B-factories.
