The cross-linking of three different paraffin waxes - a hard oxidised wax, a medium wax, and a hard wax with narrow molar mass distribution - in the presence of potassium persulphate (PPS) was investigated thermoanalytically. DSC and TG curves for untreated waxes and waxes treated with different amounts of PPS were obtained and the observations were compared with gel content data obtained through gravimetric analysis. Although initial indications were that cross-linking did occur, reheat curves of wax/PPS mixtures as well as gel content data showed that no cross-linking occurred. It was, however, found that PPS most probably decomposed into KHSO4 and that this decomposition gave rise to functionalisation of the waxes.