Abstract: An improved masterbatch of polymer, oil and carbon black is provided, and a process for the manufacture thereof, in which the polymer contains reactive groups and the masterbatch contains a crosslinking agent reactive with the reactive groups of the polymer in sufficient amount to form a low concentration of crosslinks in order to increase the strength of the polymer, the crosslinks being easily broken by the action of shear and/or heat and reformable thereafter, so that high levels of oil and carbon black can be incorporated into the masterbatch.