  Black hole X-ray binaries (BHXBs) show rich phenomenology in the spectral and
timing properties. We collected the spectral data of 20 BHXBs from the
literature across different spectral states. The spectral properties are
studied in the forms of the inner disc temperature ($T_{\rm in}$), photon index
($\Gamma$), hot electron temperature ($kT_{\rm e}$), X-ray flux ($F_{\rm X}$)
and luminosity ($L_{\rm X}$). We studied various correlations among different
spectral parameters to understand the accretion process on a global scale. In
the thermal soft states (TSS), we find most of the sources followed $F_{\rm
disc} \propto T_{\rm in}^4$ relation. A `V'-shaped correlation is found between
$\Gamma$ and total luminosity ($L_{\rm tot}$) in the hard Comptonized state
(HCS). The Comptonized luminosity is observed to be correlated with the disc
luminosity in the HCS and TSS. No notable correlation is observed in the
intermediate state (IMS). The evolution of the inner disc radius ($R_{\rm in}$)
is unclear in the HCS and IMS. We also discuss how the hot electron temperature
changes with other spectral parameters. We observe that the iron line flux
correlates with disc and Comptonized fluxes. The strength of the reprocessed
emission is found to vary across spectral states.
