The present invention provides a novel oil tackifier that can exhibit a thickening effect on oils used in cosmetics, and a novel oil-soluble copolymer that can be used for the tackifier and the like. The oil tackifier for cosmetic materials of the present invention is an oil-soluble copolymer, which includes a monomer unit containing a hydrophilic monomer, a monomer unit containing a hydrophobic monomer that is easy to crystallize, and a hydrophobic resin that contains difficult to crystallize. Monomeric unit.本發明提供一種對化妝料中使用之油分可呈現增黏效果之新穎的油增黏劑、及可用於該增黏劑等之新穎的油溶性共聚物。本發明之化妝料用油增黏劑係一種油溶性共聚物，其包含含有親水性單體之單體單元、含有易結晶性之疏水性單體之單體單元、及含有難結晶性之疏水性單體之單體單元。
