We determine the basic physical characteristics of eight Gamma-Ray Bursts (GRB) – 980519, 990123, 990510, 991028, 991216, 000301c, 000926 and 010222 – by modelling the broadband emission of their afterglows. We find that the burst kinetic energies after the GRB phase are well clustered around a mean value of 3 × 10 ergs. In contrast, the energy release in γ-rays, after correcting for collimated...