  We investigate the lack of observed low mass black hole binary systems at
short periods ( < 4 hours) by comparing the observed orbital period
distribution of 17 confirmed low mass Black hole X-ray Binaries (BHXBs) with
their implied period distribution after correcting for the effects of
extinction of the optical counterpart, absorption of the X-ray outburst and the
probability of detecting a source in outburst. We also draw samples from two
simple orbital period distributions and compare the simulated and observed
orbital period distributions. We predict that there are >200 and <3000 binaries
in the Galaxy with periods between 2 and 3 hours, with an additional ~600
objects between 3 and 10 hours
