  We investigate the energy dependencies of X-ray quasi-periodic oscillations
in black hole X-ray binaries. We analyze RXTE data on both the low- and
high-frequency QPO. We construct the low-f QPO energy spectra, and demonstrate
that they do not contain the thermal disk component, even though the latter is
present in the time averaged spectra. The disk thus does not seem to
participate in the oscillations. Moreover the QPO spectra are harder than the
time averaged spectra when the latter are soft, which can be modeled as a
result of modulations occurring in the hot plasma. The QPO spectra are softer
than the time averaged spectra when the latter are hard. The absence of the
disk component in the QPO spectra is true also for the high-frequency
(hecto-Hz) QPO observed in black hole binaries. We compute the QPO spectra
expected from the model of disk resonances.
