  The spontaneous baryogenesis mechanism by Cohen, Kaplan and Nelson is
reconsidered taking into account the transport of particles inside the
electroweak bubble walls. Using linear response theory, we calculate the
modifications on the thermal averages of the charges of the system due to the
presence of a space time dependent `charge potential' for a quantum number not
orthogonal to baryon number. The local equilibrium configuration is discussed,
showing that, as a consequence of non zero densities for conserved charges, the
$B+L$ density is driven to non zero values by sphaleronic processes. Solving a
rate equation for the baryon number generation, we obtain an expression for the
final baryon asymmetry of the Universe containing the relevant parameters of
the bubble wall, {\it i.e.} its velocity, its width, and the width of the
region in which sphalerons are active. Compared to previous estimates in which
transport effects were not taken into account, we find an enhancement of nearly
three orders of magnitude in the baryon asymmetry. Finally, the role of QCD
sphalerons in cooperation with transport effects is analyzed, showing that the
net result depends crucially on the particle species which enter into the
charge potential.
