  We discuss the basic transport phenomena in gases and plasmas obeying the
$q$-nonextensive velocity distribution (power-law). Analytical expressions for
the thermal conductivity ($K_q$) and viscosity ($\eta_q$) are derived by
solving the Boltzmann equation in the relaxation-time approximation. The
available experimental results to the ratio {$K_q$}/$\eta_q$ constrains the
$q$-parameter on the interval $0.74 \leq q \leq 1$. In the extensive limiting
case, the standard transport coefficients based on the local Gaussian
distribution are recovered, and due to a surprising cancellation, the electric
conductivity of a neutral plasma is not modified.
