From data collected around the Z resonance by the OPAL detector
at LEP, a sample of $\rm B_s^0$ decays was obtained using $\rm D_s^-\ell^+$
combinations, where the $\rm D_s^-$ was fully reconstructed in the
{\mbox{$\phi\pi^-$}}, {\mbox{$\rm K^{*0}K^-$}} and 
{\mbox{$\rm K^0_sK^-$}} decay
channels or partially reconstructed in the {\mbox{$\rm\phi\ell^-\bar{\nu}(X)$}}
decay channel.
These events were used to study $\rm B^0_s$ oscillation.
The flavor (b or $\rm \bar{b}$) at decay was determined
from the lepton charge while the flavor at production
was determined
from a combination of techniques.
The expected sensitivity of the experiment is 4.1\,ps$^{-1}$.
The experiment was not able to resolve the oscillatory
behavior, and we deduced that the $\rm B^0_s$ oscillation frequency
$\Delta m_{\rm s} > 1.0\,\rm ps^{-1}$ at the 95\% confidence level.