The response of poly(ethylene-co-1,9-decadiene) to peroxide treatment was examined and compared with a reference. The polymers were produced in a low-pressure process using a chromium-based catalyst giving a relatively high level of inherent unsaturations through thermal termination of the polymerisation. The copolymerisation with 1,9-decadiene gave an additional 63% vinyl end groups in the polymer. A great improvement in the response to dicumyl peroxide was observed for the decadiene polymers leading to a considerably smaller need for peroxide in order to obtain a certain gel content. The reason for the improved response was previously found to be the overall higher amount of vinyl groups as well as the placement of these groups along the molecular weight distribution. The remaining amount of vinyls after crosslinking was found to be exponentially dependent on the amount of peroxide added. At high peroxide levels almost all vinyl groups were consumed. The peroxide-induced consumption of vinyls was found to increase linearly with the original amount of vinyl unsaturations. At high peroxide levels, approximately the same gel content was obtained in all samples, leading to a considerably higher consumption of vinyls in the decadiene samples as compared to the reference. Mechanical measurements indicate a higher crosslinking density for the materials containing decadiene as compared to the reference. However, at lower gel contents, e.g. 40% and below, the situation is the opposite.