  We present results of the instability analysis of the post-main sequence
massive star models against radial and nonradial pulsations. We confirm that
both p- and g-modes can be excited by the $\kappa$-mechanism acting in the
metal opacity bump. However, as opposed to the previous claims, we find that an
intermediate convective zone (ICZ) related to the hydrogen burning shell is not
necessary for excitation of g-modes. These modes can be reflected at a minimum
of the Brunt-V\"ais\"al\"a frequency, located at the top of the chemical
composition gradient region surrounding the radiative helium core. This minimum
is associated with the change of actual temperature gradient from the adiabatic
value in the semiconvective zone to the radiative value above it. Thus, the
existence of pulsations at this evolutionary stage does not prove the existence
of the convective zone but only some reflective layer. Finally, we show that no
regular patterns can be expected in oscillation spectra of blue supergiant
pulsators but there is a prospect for identification of the mode degree,
$\ell$, from multicolour photometry.
