  Studies of \textit{BATSE} bursts \citep{kouveliotou:93} have resulted in the
widespread adoption of a two-group categorization: long bursts (those with
durations $\geq 2$ seconds) and short bursts (those with durations $\leq 2$
seconds). This categorization, one must recall, used the observed $T_{90}$ time
durations for bursts (during which 90\% of a burst's fluence is measured). In
this work, we have explored two ideas: 1) a statistical search for a possible
third, intermediate category of bursts (between the "short" and the "long"
ones) among 2041 \textit{BATSE} GRBs and 757 \textit{Swift/BAT} ones, 2) a
study of bursts' intrinsic durations, where durations in the bursts' reference
frames (instead of the observed durations) are considered, for this, 248
\textit{Swift/BAT} bursts that have redshift measurements were statistically
analyzed for the same categorization goal.
  We first use a Monte Carlo method to determine the proper binning of each
GRB, considering that bursts come with different uncertainties on their
durations. Then, using the method of minimization of chi-square $\chi^2$, we
search for the best fit of the normalized frequency distributions
$\frac{1}{N_0}\frac{dN}{d\ln{T}}$ of durations, this allows us to compare fits
with two groups ("short" and "long") with fits with three groups ("short",
"long", and "intermediate"). Our results indicate that the distributions of
observed durations are better fitted by three groups than two groups for
\textit{Swift/BAT} data, interestingly, the "intermediate" group appears rather
clearly for both observed and intrinsic durations. For BATSE data, the
statistical test does not prefer three groups over two. We discuss the results,
their possible underlying causes, and reasonable interpretations.
