  Kinematical and luminosity relations for black-hole jet sources are reviewed.
If the TeV flares observed from PKS 2155-304 in 2006 July are assumed to
originate from a black hole with mass $\approx 10^8 M_8 M_\odot$, then the
$\sim 5$ minute variability timescale is consistent with the light-travel time
across the Schwarzschild radius of the black hole if $M_8\sim 1$. The absolute
jet power in a synchrotron/SSC model exceeds, however, the Eddington luminosity
for a black hole with $M_8\sim 1$ unless the jet is highly efficient. The
maximum Blandford-Znajek power is $\sim 10^{46}M_8$ ergs s$^{-1}$ if the
magnetic-field energy density threading the horizon is equated with the
luminous energy density in the vicinity of the black hole. An external Compton
component can relax power requirements, so a black hole with mass $\sim 10^8
M_\odot$ could explain the observed flaring behavior. For the Swift and HESS
data taken in 2006 July, relativistic outflows with bulk Lorentz factor $\Gamma
\gtrsim 30$ satisfy $\gamma$-$\gamma$ attenuation limits. If this system
harbors a binary black hole, then the accretion disk from a more massive, $\sim
10^9 M_\odot$ black-hole primary would make an additional external radiation
component. Dual thermal accretion disk signatures would confirm this scenario.
