  Using measured X-ray luminosities to 17 Gamma-Ray Bursts (GRBs) during the
afterglow phase and accounting for radiative losses, we calculate the kinetic
energy of these bursts and investigate its relation to other GRB properties. We
then use the observed radiated energy during the prompt phase to determine the
radiative efficiency of these bursts, and explore how the efficiency relates to
other GRB observables. We find that the kinetic energy in the afterglow phase
is directly correlated with the radiated energy, total energy as well as
possibly the jet opening angle and spectral peak energy. More importantly, we
find the intriguing fact that the efficiency is correlated with the radiated
energy, and mildly with the total energy, jet opening angle and spectral peak
energy. XRF020903 also seems to follow the trends we find for our GRB sample.
We discuss the implications of these results for the GRB radiation and jet
models.
