  We study a problem of data packet transport in scale-free networks whose
degree distribution follows a power-law with the exponent $\gamma$. We define
load at each vertex as the accumulated total number of data packets passing
through that vertex when every pair of vertices send and receive a data packet
along the shortest path connecting the pair. It is found that the load
distribution follows a power-law with the exponent $\delta \approx 2.2(1)$,
insensitive to different values of $\gamma$ in the range, $2 < \gamma \le 3$,
and different mean degrees, which is valid for both undirected and directed
cases. Thus, we conjecture that the load exponent is a universal quantity to
characterize scale-free networks.
