  Past studies suggest that long-duration gamma-ray bursts (GRBs) have a
standard energy of E_gamma ~ 10^51 erg in ultra-relativistic ejecta when
corrected for asymmetry ("jets"). However, recently a group of sub-energetic
bursts, including the peculiar GRB 980425 associated with SN 1998bw (E_gamma ~
10^48 erg), has been identified. Here we report radio observations of GRB
030329, the nearest burst to date, which allow us to undertake calorimetry of
the explosion. Our observations require a two-component explosion: a narrow (5
degrees) ultra-relativistic component responsible for the gamma-rays and early
afterglow, and a wide, mildly relativistic component responsible for the radio
and optical afterglow beyond 1.5 days. While the gamma-rays are energetically
minor, the total energy release, dominated by the wide component, is similar to
that of other GRBs. Given the firm link of GRB 030329 with SN 2003dh our result
suggests a common origin for cosmic explosions in which, for reasons not
understood, the energy in the highest velocity ejecta is highly variable
