  We discuss the matching procedure for heavy-light 4-quark operators using the
Fermilab method for heavy quarks and staggered fermions for light quarks. These
ingredients enable us to construct the continuum-limit operator needed to
determine the oscillation frequency of neutral B mesons. The matching is then
carried out at the one-loop level. We also present an updated preliminary
result for the SU(3)-breaking ratio \xi, based on calculations using the MILC
Collaboration's ensembles of lattice gauge fields.
