  We model jets in low-luminosity (FR I) radio galaxies as intrinsically
symmetrical, axisymmetric, decelerating relativistic flows with transverse
velocity gradients. This allows us to derive velocity fields and the
three-dimensional distributions of magnetic-field ordering and rest-frame
emissivity. A conservation-law analysis, combining the kinematic model with
X-ray observations of the surrounding IGM, gives the profiles of internal
density, pressure, Mach number and entrainment rate along the jets. We
summarize our recently-published results on 3C 31 and outline new work on other
sources and adiabatic jet models.
