  We examine limits to the efficiency for particles acceleration in shearing
flows, showing that relativistic flow speeds are required for efficient gradual
shear acceleration. We estimate maximum achievable particle energies for
parameters applicable to relativistic AGN jets. The implications of our
estimates is that if large-scale jets are relativistic, then efficient electron
acceleration up to several PeV, and proton acceleration up to several EeV
energies appears feasible. This suggests that shear particle acceleration could
lead to a continued energization of synchrotron X-ray emitting electrons, and
be of relevance for the production of ultra-high-energy cosmic-ray particles.
