  We extend our previous studies to calculate the B meson B parameters B_B and
B_S on the lattice, and present an update of the results for the B_s meson
width difference. We perform an extensive study of systematic errors in the
quenched calculation of the B-parameters, and find that the systematic errors
are in good control using the NRQCD action for heavy quark. We also report our
preliminary results from unquenched simulations.
