  The onset of synchronization in a system of random frequency oscillators
coupled through a random network is investigated. Using a mean-field
approximation, we characterize sample-to-sample fluctuations for networks of
finite size, and derive the corresponding scaling properties in the critical
region. For scale-free networks with the degree distribution $P(k)\sim
k^{-\gamma}$ at large $k$, we found that the finite size exponent $\bar{\nu}$
takes on the value 5/2 when $\gamma>5$, the same as in the globally coupled
Kuramoto model. For highly heterogeneous networks ($3<\gamma <5$), $\bar{\nu}$
and the order parameter exponent $\beta$ depend on $\gamma$. The analytic
expressions for these exponents obtained from the mean field theory are shown
to be in excellent agreement with data from extensive numerical simulations.
