  The death of massive stars and the processes which govern the formation of
compact remnants are not fully understood. Observationally, this problem may be
addressed by studying different classes of cosmic explosions and their energy
sources. Here we discuss recent results on the energetics of gamma-ray bursts
(GRBs) and Type Ib/c Supernovae (SNe Ib/c). In particular, radio observations
of GRB030329, which allow us to undertake calorimetry of the explosion, reveal
that some GRBs are dominated by mildly relativistic ejecta such that the total
explosive yield of GRBs is nearly constant, while the ultra-relativistic output
varies considerably. On the other hand, SNe Ib/c exhibit a wide diversity in
the energy contained in fast ejecta, but none of those observed to date (with
the exception of SN1998bw) produced relativistic ejecta. We therefore place a
firm limit of 3% on the fraction of SNe Ib/c that could have given rise to a
GRB. Thus, there appears to be clear dichotomy between hydrodynamic (SNe) and
engine-driven (GRBs) explosions
