The measurement of the B_s mixing oscillation frequency, Delta
m_s, has been the main goal for both experiments CDF and D0 which are
running at the Tevatron collider.  With 1 fb-1 of data collected during the
last four years D0 set a lower and upper limit on this frequency, 17 < Delta
m_s < 21 ps-1.  CDF measured Delta m_s with a precision better than 2% and
the probability that the data could randomly fluctuate to mimic such a
signature is 0.2%.