Abstract: A hydrocarbon resin is prepared by (1) thermally polymerizing a mixture consisting essentially of (a) about 40% to 90% by weight based on total monomers of a cyclic diolefin component comprising at least about 50% by weight dicyclopentadiene, and (b) about 60% to 10% by weight based on total monomers of a specified vinyl aromatic component, preferably alpha-methylstyrene; para-methyl-.alpha.-methylstyrene; 2,4-diphenyl-4-methyl-1-pentene, or mixtures thereof, and (2) recovering a product having a Ring and Ball softening point of about 70.degree. to about 150.degree. C. Hydrogenation of this resin produces light colored, thermally stable products that are useful as tackifiers in adhesives.