Abstract: High softening point resins are prepared by a process which comprises polymerizing in the presence of a Friedel-Crafts catalyst a mixture of (1) a feedstock comprising C.sub.5 olefins and diolefins, C.sub.6 olefins and diolefins or a mixture of C.sub.5 and C.sub.6 olefins and diolefins, said feedstock being obtained from the steam-cracking of petroleum feedstock and (2) a polymer obtained by the thermal or cationic polymerization of dicyclopentadiene, an alkyl cyclopentadiene dimer, a codimer of cyclopentadiene with an alkyl cyclopentadiene, a codimer of cyclopentadiene or an alkyl cyclopentadiene with a C.sub.5 or a C.sub.6 conjugated linear or non-cyclic diolefin, or a mixture of said dimer and codimers. The resin may be mixed with rubber to make a pressure-sensitive adhesive.