  Galactic binary systems that contain a black hole candidate emit hard X-rays
in their low luminosity mode. We show that this emission can be understood as
due to the Compton scattering of photons from the companion star and/or the
accretion disk by relativistic electrons in a jet. The same electrons are also
responsible for the radio emission. Two sources -- XTE J1118+480 and Cygnus X-1
-- are modelled as representatives of black holes with low and high luminosity
companion stars respectively. We further show that the ultraluminous compact
X-ray sources observed in nearby galaxies have the properties expected of
stellar mass black holes with high luminosity companions in which the jet is
oriented close to our line of sight.
