  We study spectral variability of 11 ultraluminous X-ray sources (ULX) using
archived XMM-Newton and Chandra observations. We use three models to describe
the observed spectra; a power-law, a multi-colour disk (MCD) and a combination
of these two models. We find that out of the 11 ULXs in our sample, 7 ULXs show
a correlation between the luminosity and the photon index Gamma (hereafter
L-Gamma correlation). Furthermore, out of the 7 ULXs that have the L-Gamma
correlation, 4 ULXs also show spectral pivoting in the observed energy band. We
also find that two ULXs show an L-Gamma anti-correlation. The spectra of 4 ULXs
in the sample can be adequately fitted with a MCD model. We compare these
sources to known black hole binaries (BHB) and find that they follow similar
paths in their luminosity-temperature (hereafter L-T) diagrams. Finally we show
that the 'soft excess' reported for many of these ULXs at 0.2 keV seem to
follow a trend L \propto T^{-4} when modeled with a power-law plus a 'cool' MCD
model. This is contrary to the expected L \propto T^4 relation that is expected
from theory and what is seen for many accreting BHBs.
