While there is essentially overwhelming evidence that X-ray emission from FRI galaxy jets comes from the synchrotron process, the situation for X-ray emission from jets of high luminosity radio sources is unclear. The crux of the solution hinges on the typical value of the velocity of the emitting plasmas. If the bulk Lorentz factors, Gamma, are moderate to small (<=5), then the inverse Compton (IC/CMB) emission model is inadequate and some alternative such as non-standard synchrotron models is required. If Gamma >= 10, the intrinsic emitted power is greatly reduced even though the total jet power is large. We will discuss these problems in the context of how to estimate the underlying jet characteristics when most observational data provide information only on the emitting plasma. Recent Chandra data, will be included where relevant.