Abstract: Oil-soluble, phenolic resin-modified natural resinic acid esters, which are able to form self-gelling mineral oil solutions and in the form of gel varnishes can advantageously be used as binder resins in printing inks for offset printing and letterpress printing, and also processes for their preparation from natural resins, phenols, aldehydes, condensation catalyst, esterifying agents and modifiers by reaction of the components at temperatures in the range from 80.degree. to 300.degree. C., individual components preferably being initially introduced and the other components being metered in, the combined use of a magnesium compound as condensation catalyst and the continuous removal of the water of reaction during the condensation reaction by azeotropic distillation with co-use of an inert organic solvent as distillative entraining agent being necessary and decisive for the self-gelling property of the process product.