  Our work focuses on a comprehensive orbital phase dependent spectroscopy of
the four High Mass X-ray Binary Pulsars (HMXBPs) 4U 1538-52, GX 301-2, OAO
1657-415 & Vela X-1. We hereby report the measurements of the variation of the
absorption column density and iron-line flux along with other spectral
parameters over the binary orbit for the above-mentioned HMXBPs in elliptical
orbits, as observed with the Rossi X-ray Timing Explorer (RXTE) and the
BeppoSAX satellites. A spherically symmetric wind profile was used as a model
to compare the observed column density variations. Out of the four pulsars,
only in 4U 1538-52, we find the model having a reasonable corroboration with
the observations, whereas in the remaining three the stellar wind seems to be
clumpy and a smooth symmetric stellar wind model appears to be quite inadequate
in explaining the data. Moreover, in GX 301-2, neither the presence of a disk
nor a gas stream from the companion was validated. Furthermore, the spectral
results obtained in the case of OAO 1657-415 & Vela X-1 were more or less
similar to that of GX 301-2.
