  We present an analysis of the nebular spectra of 103 stripped envelope (SE)
supernovae (SNe) collected from the literature and observed with the Subaru
Telescope from 2002 to 2012, focusing on [O I] 6300, 6363. The line profile and
width of [O I] are employed to infer the ejecta geometry and the expansion
velocity of the inner core. These two measurements are then compared with the
SN sub types, and further with the [O I]/[Ca II] ratio, which is used as an
indicator of the progenitor CO core mass. Based on the best fit results of the
[O I] profile, the objects are classified into different morphological groups,
and we conclude that the deviation from spherical symmetry is a common feature
for all types of SESNe. There is a hint (at about 1 sigma level) that the
distributions of the line profile fractions are different between canonical
SESNe and broad-line SNe Ic. A correlation between [O I] width and [O I]/[Ca
II] ratio is discerned, indicating that the oxygen-rich material tends to
expand faster for objects with a more massive CO core. Such a correlation can
be utilized to constrain the relation between the progenitor mass and the
kinetic energy of the explosion. Further, when [O I]/[Ca II] ratio increases,
the fraction of objects with Gaussian [O I] profile increases, while those with
double-peaked profile decreases. This phenomenon connects ejecta geometry and
the progenitor CO core mass.
