  Using theoretical tools developed by the JET Collaboration in which one
employes 2+1D or 3+1D hydrodynamic models for the bulk medium evolution and jet
quenching models, the combined data on suppression of single inclusive hadron
spectra at both RHIC and LHC are systematically analyzed with five different
approaches to the parton energy loss. The jet transport parameter is extracted
from the best fits to the data with values of $\hat q \approx 1.2\pm 0.3$ and
$1.9\pm 0.7$ GeV$^2$/fm in the center of the most central Au+Au collisions at
$\sqrt{s}=200$ GeV and Pb+Pb collisions at $\sqrt{s}=2.67$ TeV, respectively at
an initial time $\tau_0=0.6$ fm/$c$ for a quark jet with an initial energy of
10 GeV/$c$.
