  We fit the broad-band X/gamma-ray spectrum (0.8-1000 keV) of the accreting
black hole XTE J1550-564 in the very high state. The quasi-simultaneous data
from ASCA, RXTE and OSSE show that the disc is strongly Comptonized, with a
high energy tail extending out to several hundreds keV. However, inverse
Compton scattering by a purely thermal or purely power-law electron
distribution cannot explain the observed spectrum. Instead the data require a
hybrid distribution, with both thermal and non-thermal electrons scattering the
disc photons. This is very similar to the electron distribution inferred for
other high and very high state black hole binaries, showing that it is a
generic feature of high mass accretion rate black holes.
