  I summarize the observables constraining the B_s-B_s-bar mixing complex and
present a new calculation of the element Gamma_{12}^s of the decay matrix.
Gamma_{12}^s enters the prediction of the width difference Delta Gamma_s, for
which we obtain Delta Gamma_s^SM = 0.088 +/- 0.017 ps^(-1), if no new physics
enters B_s-B_s-bar mixing. Applying our formulae to Tevatron data we find a
deviation of the B_s-B_s-bar mixing phase phi_s from its Standard Model value
by 2 standard deviations. I stress that present data do not give any
information on the sign of Delta Gamma_s.
