  We use an appropriate combination of moments of finite energy sum rules in
QCD in order to compute the B_q-meson decays constants f_B and f_{B_s}.We
perform the calculation using a two-loop computation of the imaginary part of
the pseudoscalar two point function in terms of the running bottom quark mass.
The results are stable with the so called QCD duality threshold and they are in
agreement with the estimates obtained from Borel transform QCD sum rules and
lattice computations.
