The influence of oxidised and graphitised carbon black on the degree of crosslinking has been investigated for two different crosslinking systems: peroxide and high pressure vulcanisation (HPV), The latter includes also high temperature, but not any vulcanisation chemicals. It was found that peroxide yielded lower degrees of crosslinking when oxidised carbon black was used while HPV polybutadienes showed the opposite behaviour. It is suggested that strong polymer - carbon black interactions are evolved in HPV, increasing the apparent crosslink density as measured by swelling.