Abstract: A process for producing a hydrocarbon resin (C) which comprises copolymerizing 100 parts by weight of vinyl aromatic hydrocarbons (A) containing more than 80% by weight isopropenyltoluene and from about 5 to 100 parts by weight of a fraction (B) which is the by-product of cracking or refining petroleum and mainly comprising unsaturated hydrocarbons having a boiling point ranging from about -15.degree.C to 45.degree.C and having 4 to 5 carbon atoms in the presence of a Friedel-Crafts catalyst and pressure-sensitive adhesives comprising the hydrocarbon resin produced in combination with a rubber.