  We suggest that low-redshift XBLs (X-ray selected BL Lacertae objects) may be
the only extragalactic gamma-ray sources observable at TeV energies. We use
simple physical considerations involving synchrotron and Compton component
spectra for blazars to suggest why the observed TeV sources are XBLs, whereas
mostly RBLs and FSRQs are seen at GeV energies. These considerations indicate
that the differences between XBLs and RBLs cannot be explained purely as
relativistic jet orientation effects. We note that the only extragalactic TeV
sources which have been observed are XBLs and that a nearby RBL with a very
hard spectrum in the GeV range has not been seen at TeV energies. We also note
that of the 14 BL Lacs observed by EGRET, 12 are RBLs, whereas only 2 are XBLs.
We give a list of nearby XBLs which we consider to be good candidate TeV
sources and predict estimated TeV fluxes for these objects.
