  We have investigated the influence of several line overlaps between 28SiO,
29SiO and 30SiO on maser emission from the envelopes of late-type stars using
the Large Velocity Gradient radiative transfer formalism modified to account
for overlaps. Our model includes: (i) 40 rotational levels for each of the v=0
to 4 vibrational states and each isotopic species; (ii) collisions with
molecular and atomic hydrogen; and (iii) radiative pumping by a shell of dust
grains surrounding the SiO masing layers.
  We have shown that several line overlaps may play a role on the excitation of
the 28SiO v=3, J=1-0 maser, and on the anomalously weak v=3, J=2-1 emission. We
suggest that 28SiO maser emission in the v=4, J=5-4 line, the only one observed
in this vibrational level, may also result from line overlaps. For 29SiO,
infrared line overlaps successfully explain observed maser emission in the v=0,
J=5-4 and v=1, 2, J=6-5 lines. 30SiO, v=0, J=2-1, and v=0, J=4-3 maser
emissions could also result from line overlaps, and we find that several
overlaps could explain the newly discovered maser line 30SiO v=1, J=1-0.
Finally, we make some predictions for new 28SiO, 29SiO and 30SiO maser lines.
