  We studied all blazars of known redshift detected by the Fermi satellite
during its first three months survey. For the majority of them, pointed Swift
observations ensures a good multiwavelength coverage, enabling us to to
reliably construct their spectral energy distributions (SED). We model the SEDs
using a one-zone leptonic model and study the distributions of the derived
interesting physical parameters as a function of the observed gamma-ray
luminosity. We confirm previous findings concerning the relation of the
physical parameters with source luminosity which are at the origin of the
blazar sequence. The SEDs allow to estimate the luminosity of the accretion
disk for the majority of broad emitting line blazars, while for the line-less
BL Lac objects in the sample upper limits can be derived. We find a positive
correlation between the jet power and the luminosity of the accretion disk in
broad line blazars. In these objects we argue that the jet must be
proton-dominated, and that the total jet power is of the same order of (or
slightly larger than) the disk luminosity. We discuss two alternative scenarios
to explain this result.
