  SN 1998bw holds the record for the most energetic Type Ic explosion, one of
the brightest radio supenovae and probably the first supernova associated with
a gamma-ray burst. In this paper we present spectral observations of SN 1998bw
observed in a cooperative monitoring campaign using the AAT, UKST and the SSO
2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94
days after V_band maximum in comparison to well-studied examples of Type Ic SNe
in order to quantify the unusual properties of this supernova event. Though the
early spectra differ greatly from the observations of classical Ic SNe, we find
that the evolution from the photospheric to the nebular phases is slow but
otherwise typical. The spectra differ predominantly in the extensive line
blending and blanketing which has been attributed to the high velocity of the
ejecta. We find that by day 19, the absorption line minima blueshifts are 10% -
50% higher than other SNe and on day 94 emission lines are 45% broader, as
expected if the progenitor had a massive envelope. However, it is difficult to
explain the extent of line blanketing entirely by line broadening, and we argue
that additional contribution from other species is present, indicating unusual
relative abundances or physical conditions in the envelope.
